ESOS: the Energy Savings Opportunity Scheme
ESOS meaning: ESOS stands for the Energy Savings Opportunity Scheme (often written “energy saving opportunity scheme”) — the UK’s mandatory energy-audit scheme for large organisations, administered by the Environment Agency.
Phase 4 is the cycle running now: qualification on 31 December 2026, notification by 5 December 2027 [2].
What ESOS asks of you, in plain English
Four things, in order. Everything else on this page is detail hanging off one of them.
ESOS does not require you to act on what the audit finds. It requires you to find it, have it checked, and say so.
That is the scheme as it is announced.
Below is what it does to a company that reads it late.
The group that was sure ESOS did not apply to it
An illustrative case — not a real company.
A privately held UK holding company with four trading subsidiaries: a light-manufacturing business, two regional distributors and a small property arm.
None of the four employs 250 people. None of the four turns over £44 million.
The finance director checked this in 2023, concluded ESOS was a large-company scheme, and moved on.
In March 2026 the group acquires a fifth business. Headcount across the UK group passes 250 in August.
On 31 December 2026 — a date nobody in the group has in a calendar — the group qualifies.
It qualifies because ESOS tests the group, not the subsidiary. GOV.UK puts it without any hedging: “If a corporate group contains at least one undertaking in the UK which meets the qualification conditions, its entire UK operation must take part in ESOS.” [2]
That last line is the one that costs money.
By the time the group finds out, the 12 months of metered data it needs to audit are already partly in the past, and reconstructing them from invoices is slower and more expensive than collecting them would have been.
The way out is not urgency. It is knowing which date starts the clock.
ESOS penalties — what each failure is worth
ESOS is enforced through civil penalties, not prosecution. The amounts below are statutory maxima, set out in Part 8 of the ESOS Regulations 2014 (regulations 43 to 47). They do not appear anywhere on the GOV.UK guidance page.
Two of those are worth separating, because almost every summary online merges them.
Missing the deadline is the £5,000 breach. Not doing the audit at all is the £50,000 one.
A company that is late but has done the work is in a materially different position from one that has not started, and the penalty structure says so.
There is one relief worth knowing: an organisation in its first compliance period faces a reduced initial penalty of up to £5,000 for failing to undertake an assessment, rather than the full £50,000 [3].
Our full breakdown of amounts, appeals and the route back into compliance is in ESOS penalties and fines.
How the Environment Agency actually sets a penalty
Not at the maximum. The regulator publishes a stepped method, and it starts at the statutory ceiling and works down.
Then there is the part that is not money.
Every penalty may carry a publication penalty: the breach, and the name of the organisation, go on a public register, and the Environment Agency publishes the climate-change civil penalties dataset in the open [28].
For most of the finance directors who read this page, that is the sanction that concentrates the mind, not the £50,000.
The three instruments that make up ESOS regulations today
ESOS is not one document. It is a 2014 instrument amended twice, and the second amendment is six weeks old.
What SI 2026/701 changed, in the explanatory note’s own terms [6]:
Two changes there are deferred rather than delivered, and it is worth being exact about which.
The government’s plan to refocus ESOS on net zero as well as energy efficiency, and to realign the qualification thresholds with SECR, were both postponed to Phase 5 [1].
Any page telling you ESOS Phase 4 is a net-zero scheme is describing something that has not been legislated. The statutory basis, phase by phase, is in ESOS legislation, and the instrument itself is set out in SI 2014/1643 and every amendment to 2026.
ESOS compliance — who actually has to do it
One date, one test, and a group rule that catches more organisations than the test itself does.
A large undertaking is, in the phase 4 guidance’s exact words, “any UK undertaking that meets either one or both of the following conditions: 1. It employs 250 or more people… 2. It has an annual turnover in excess of £44 million and an annual balance sheet total in excess of £38 million.” [2]
Read the logic carefully, because it is not symmetrical.
Now the group rule, which is where most late discoveries happen.
The test runs on the highest UK parent — “the undertaking which has no parent, or only has parents which are overseas undertakings” — and if any UK undertaking in that group qualifies, the whole UK operation is in.
Overseas ownership does not get you out of it. Where a global group contains more than one highest UK parent group, GOV.UK is explicit: “If one highest UK parent group is in scope of ESOS then every other highest UK parent group in the same global group must also participate in ESOS.” [2]
By default the highest UK parent is the responsible undertaking: it does the assessment and notifies for itself and its subsidiaries. Another undertaking in the group can take the role instead, provided every undertaking in the group agrees in writing.
The edge cases — joint ventures, franchises, trusts, partial-year acquisitions — are in ESOS requirements, and the exclusions are in ESOS exemptions. The thresholds themselves, and the “and” test that decides them, are in ESOS qualification.
Do you qualify for ESOS Phase 4?
Up to four questions against the statutory test, measured where the regulations measure it — across the highest UK parent group, on 31 December 2026.
Nothing is sent anywhere. The whole check runs in your browser.
The four ESOS phases, and the two dates live now
ESOS runs in recurring four-year compliance periods. Three have closed. Phase 4 is the one you are in.
Two of those need saying out loud, because they are the two most commonly misstated ESOS facts on the web.
Phase 3’s compliance date is 5 June 2024, not 5 December 2023. The six-month move was made in legislation before the original date fell, so both dates are “real” — but only one of them is the compliance date.
6 December 2023 is not a deadline at all. It is the day the Phase 4 compliance period opened. Every date-by-date obligation is in ESOS deadlines, and every compliance period from 2014 to 2031 is mapped in ESOS phases.
The routes that survive into Phase 4 — and the two that do not
Phase 3 offered four ways to cover your energy. Phase 4 offers two, plus an exemption that did not exist before.
Before the routes, the obligation they discharge.
ESOS asks you to identify savings, not to install them — and since 2023 to publish an action plan saying what you intend to do about them, and to report progress against it — see ESOS progress reports.
That distinction is the whole design of the scheme, and it is the thing most summaries get wrong.
If you complied in Phase 3 using DECs, this is the single change on this page that will cost you money, and there is a reasonable chance nobody has told you.
GOV.UK states the removal plainly: “Display Energy Certificates (DECs) and Green Deal Assessments (GDAs) have been removed as alternative compliance routes in the fourth compliance period, meaning they cannot be used as a substitute for an energy audit for those buildings to which they apply.” [2]
On the common ISO 50001 vs ESOS question: they are not competing regimes. A certified energy management system is an ESOS compliance route for the consumption it covers — and from Phase 4, where all of your total or significant energy consumption falls under it, it discharges the audit and the lead assessor duty as well.
Note what actually moved. SI 2026/701 widened the trigger in regulation 33(2A) from total energy consumption alone to total or significant. The old “100% of your energy supplies” formulation is dead — and GOV.UK’s own ESOS overview, last updated 16 February 2026, still serves it.
Which twelve months count
This is the most misunderstood rule in ESOS, and the one that quietly makes a company’s own financial year unusable.
The compliance period is four years. The reference period is twelve months — a different thing, doing a different job, and the two get merged constantly.
The rule, verbatim: “You must calculate your total energy consumption over a reference period of 12 consecutive months. The reference period must include the qualification date and end on or before the compliance date.” [2]
For Phase 4 that means twelve consecutive months which contain 31 December 2026 and end on or before 5 December 2027.
Work it through and the window is narrower than it sounds: your period must start somewhere between 1 January 2026 and 6 December 2026.
Which is why a December year-end company cannot use its 2027 financial year, and a March year-end company must use 2026/27 rather than 2025/26.
The energy audit and the 95% rule
You do not have to audit everything. You have to audit almost everything, and account for the rest.
The requirement, verbatim: “You are required to cover assets and activities accounting for not less than 95% of your total energy consumption by a route to compliance… The maximum 5% of total energy consumption that may be excluded from any audit or alternative compliance measures is known as your ‘de minimis’ energy consumption.” [2]
Total energy consumption means all the energy you buy, across all four of the scheme’s organisational purposes.
On transport, the test is who buys the fuel, not who takes the journey.
GOV.UK: “You are required to include transport where your organisation is supplied with the fuel for business purposes. However, this does not apply where you procure a transportation service that includes an indirect payment for the fuel consumption.” [2]
Everything you exclude has to be written down. Where you estimate rather than meter, you must notify the scheme administrator, and keep the reason and the method in the evidence pack.
What the audit itself has to contain — site coverage, energy intensity ratios, the costed opportunities — is in the ESOS energy audit guide, and the assessment as a whole in ESOS assessment.
Who signs it, and when you do not need one
The lead assessor is the scheme’s quality control: an individual on an approved register who reviews the assessment and confirms it meets the regulations.
GOV.UK names the exemptions in one line: you must appoint a lead assessor “unless you have zero energy consumption, use less than 40,000kWh of energy or have ISO 50001 energy management system which covers at least 95% of your total energy consumption” [2].
Read that third limb against the instrument, because the guidance departs from it. Regulation 33(2A) does not turn on a percentage of total consumption. It applies where “all of the participant’s— (a) total energy consumption, or (b) significant energy consumption falls under the certified energy management system”. The 95% belongs to regulation 25(2), which defines areas of significant energy consumption as those assets and activities which together account for “not less than 95%” of total energy consumption — and it allows that to be measured in energy measurement units or by energy spend, which the guidance never mentions. Regulation 25(1) makes identifying them elective: elect, and the certificate must cover all of that band; do not elect, and it must cover the total.
All three still require a notification. An exemption from the assessor is not an exemption from the scheme.
There are seven approved registers. The list changes: the Institution of Chemical Engineers was removed on 16 February 2026, Stroma Certification in February 2025, and Quidos was added in March 2025 [1].
On competence standards, Phase 4 has an oddity worth knowing.
BSI published two new standards in February 2025 — PAS 51215-1:2025 on the assessment process and PAS 51215-2:2025 on lead assessor competencies [18].
But PAS 51215:2014 remains the competency standard for ESOS Phase 4; the 2025 competency standard is available for voluntary use when judging whether an assessor is suitable [1].
SI 2026/701 also added a duty on the assessor’s side: they must now notify their approval body when an assessment is complete, and hand over contact details for the responsible undertaking.
What to ask before you appoint one, and how the internal-versus-external choice works, is in the ESOS lead assessor guide and choosing ESOS consultants and assessors.
ESOS reporting and notification, through MESOS
The compliance act is the notification. Everything before it is preparation for one form, submitted by one date.
ESOS reporting ends in one submission: notification goes through MESOS — Manage your ESOS reporting — the Environment Agency’s online system [9].
The deadline for Phase 4 is 5 December 2027.
The evidence pack is not filed with the notification — it is held by you and produced if the regulator asks.
That is why “failure to keep records” is a separate £5,000 penalty from failing to notify: they are two different duties, and an organisation can breach the second while satisfying the first.
The screen-by-screen walkthrough is in ESOS notification, and what has to be in the report itself in ESOS reporting.
The action plan, and the updates that follow it
Phase 3 added an obligation that outlives the notification by three years. Phase 4 extended it again.
After notifying, the responsible undertaking must produce an ESOS action plan — what it intends to do about what the audit found — and then report annually against it [13].
Phase 4 also closes the loop backwards, and this is genuinely new.
SI 2026/701 inserts a new Chapter 3B requiring participants to review the action plan measures identified in the previous compliance period and report where these were not met, identifying all the measures actually taken and estimating the energy savings achieved since the previous compliance date [6].
So a Phase 3 action plan that promised measures nobody delivered now has to be explained inside the Phase 4 assessment.
If you wrote an ambitious Phase 3 action plan in 2024, this is the chapter to read twice. What goes in a plan, and what a progress update has to say, is in ESOS action plans.
Which route is yours
Two numbers decide almost every ESOS compliance strategy: how much energy you use, and how much of it an ISO 50001 certificate already covers.
Put them in and the selector applies the Phase 4 rules as amended by SI 2026/701 — including the widened ISO 50001 trigger, which now reaches total or significant energy consumption, and the zero-kWh route that did not exist before July.
It computes; it does not look anything up.
ESOS, SECR and UK SRS — one dataset, three duties
The energy figure you assemble for ESOS is the same figure two other regimes want. Almost nobody collects it once.
The 40,000 kWh line appearing in two regimes is not a coincidence — it is the same policy idea about de minimis energy users, applied twice.
The overlap that matters is the underlying data.
ESOS makes you build a complete, metered, kWh-denominated picture of everything your UK group burns over twelve months. SECR wants a subset of that annually. UK SRS S2 wants Scope 1 and 2 emissions, which are that same energy data multiplied by conversion factors.
A company doing ESOS properly in 2026–27 has, as a by-product, most of what it needs for its 2027 SECR disclosure and a defensible baseline for UK SRS S2.
The line-by-line comparison is in ESOS vs SECR, and the mapping from audit data into climate disclosure is in how ESOS energy data feeds into UK SRS S2.
Both of the deferred Phase 5 changes point the same way: a net-zero refocus and SECR-aligned thresholds would pull these three regimes closer together, not further apart.
Where the work actually lands
The regulations are sector-neutral. The effort is not, and GOV.UK offers no sector guidance at all.
On geography: ESOS work is desk-based plus site visits, and every approved register is national. There is no such thing as a regionally qualified ESOS assessor, so “ESOS consultant near me” is the wrong search — the right one is whether the assessor has done your sector.
What ten years of ESOS has actually found
The government published its second post-implementation review in July 2025. These are its numbers, and they are the only credible ones in circulation.
Two readings of those four numbers, and both are honest.
The audits found savings worth roughly 5% of participants’ total consumption — 47 TWh against 900 TWh — which is a large number in absolute terms and a modest one as a proportion.
And the scheme’s own review is candid about attribution: “only 6% of measures were directly attributed to ESOS, with 38% being at least partially attributed” [8].
That 13% gap is the enforcement population.
It is also the honest answer to the question this page’s readers actually ask, which is whether anyone is really checking: roughly 1,290 corporate groups did not notify in Phase 3, and the Environment Agency publishes the penalties it issues.
We do not publish a cost-of-compliance figure, because there is not a credible one. The 2025 review states plainly that it has no further quantitative data from participants on cost, and every number circulating online traces back to a 2015 blog post.
The sequence, from today to 5 December 2027
Not a project plan. The order in which the decisions actually constrain each other.
All of that is one scheme, one deadline and one form.
If your UK group employs 250 people, or turns over more than £44 million with a balance sheet above £38 million, on 31 December 2026, you must have 95% of your energy audited and notified to the Environment Agency by 5 December 2027.
Your reference period starts before the qualification date, not after it.
See what Phase 4 requires, step by step Or start with the dates
UKSRS — independent reference on UK sustainability and energy reporting. Every figure on this page is cited to a named primary source.
ESOS meaning — what ESOS stands for
What is ESOS? ESOS stands for the Energy Savings Opportunity Scheme — the UK’s mandatory energy-audit scheme for large organisations, administered by the Environment Agency in England, with equivalent bodies in Scotland, Wales and Northern Ireland.
Qualifying businesses must measure their total energy use and have it audited by a registered lead assessor at least once every four years, then notify the Environment Agency by the compliance deadline.
ESOS was introduced in 2014 by The Energy Savings Opportunity Scheme Regulations 2014 (SI 2014/1643), implementing Article 8 of the EU Energy Efficiency Directive in UK law. It has continued in force since Brexit, but the Directive is no longer its legal basis: the enabling power is now the Energy Act 2023, sections 254 to 260 and 263 — see ESOS legislation for the statutory basis.
Its policy origin is the 2012 UK Energy Efficiency Strategy, and the shape of Phase 4 was set by the government response to the ESOS consultation.
- Full name
- Energy Savings Opportunity Scheme
- Administered by
- Environment Agency (England); equivalent bodies in Scotland, Wales and Northern Ireland
- Current phase
- Phase 4 — 6 December 2023 to 5 December 2027
- Qualification date
- 31 December 2026
- Compliance deadline
- 5 December 2027
- Who qualifies
- 250+ employees, OR >£44m turnover AND >£38m balance sheet
- Audit coverage
- At least 95% of total energy consumption
- Penalties
- £5,000–£50,000, plus £500/day up to £40,000
ESOS is a mandatory energy assessment scheme for organisations in the UK that are large enterprises, or that are part of a large group.
GOV.UK — Energy Savings Opportunity Scheme (ESOS) guidance
Is ESOS a legal requirement?
Yes. It is a statutory duty under SI 2014/1643 as amended, enforced by the Environment Agency through civil penalties of up to £50,000 plus daily penalties and publication.
Who is required to comply with ESOS?
Any UK large undertaking, and every UK undertaking in a group containing one. The test is 250+ employees, or turnover above £44m together with a balance sheet above £38m.
What is involved in an ESOS assessment?
Measure total energy use over a 12-month reference period, audit assets and activities covering at least 95% of it, have a lead assessor sign it off, and notify through MESOS.
What is an ESOS report?
The output of the assessment: the energy calculation, the audits, the energy intensity ratios and the costed opportunities. It stays in your evidence pack — only the notification is submitted.
ESOS penalties and non-compliance fines
ESOS is enforced through civil penalties rather than criminal prosecution, and the Environment Agency sets amounts using a published stepped methodology.
The stepped approach starts from the statutory maximum for the breach, then adjusts for culpability, the size of the organisation, compliance history and cooperation.
Every penalty can be accompanied by a publication penalty — the breach is placed on a public register, and the Environment Agency publishes a climate change civil penalties dataset.
The full ladder — amounts per breach, appeals and remediation — is in ESOS penalties and fines.
ESOS compliance — the qualification thresholds
ESOS applies to any UK “large undertaking” — the test is based on staff headcount, or a combination of turnover and balance sheet size.
An organisation qualifies on the qualification date — 31 December 2026 for Phase 4 — if it is a UK large undertaking, meaning it meets at least one of two tests: it has 250 or more employees, or it has more than £44m annual turnover and more than £38m on its balance sheet.
Corporate groups qualify if the group as a whole meets either threshold, even if no single subsidiary does on its own, and overseas parent companies with a qualifying UK subsidiary are also brought into scope.
For the detailed breakdown of group structures, franchises and joint ventures, see ESOS requirements, and the dedicated ESOS exemptions guide for who falls outside scope.
ESOS Phase 4 at a glance
ESOS runs in recurring four-yearly compliance periods. Phase 4 is the current cycle, with a notification deadline of 5 December 2027.
Each phase requires qualifying organisations to carry out (or update) ESOS-compliant energy audits covering at least 95% of their total energy consumption — raised from 90% by the ESOS (Amendment) Regulations 2023 — then notify the Environment Agency via the MESOS portal by the compliance deadline.
Phase 4 tightened the regime compared with Phase 3 — see exactly what changed in the Phase 4 compliance guide — including the removal of two alternative compliance routes and a stronger expectation that organisations report on savings actually achieved.
Full date-by-date detail, including the Phase 3 progress-update deadlines, is in ESOS deadlines, and the historic cycle in ESOS Phase 3.
Searching for the “ESOS consultation”? The government’s 2021 consultation on strengthening the scheme concluded in the 2023 Amendment Regulations that shaped Phase 4, and the remaining net-zero proposals were postponed to Phase 5.
ESOS reporting — step by step to notification
Four steps take a qualifying organisation from energy measurement to a signed-off notification.
Most organisations commission a full ESOS energy audit covering their highest-consuming sites, then rely on partial audits or recognised alternatives for the remainder.
On the common ISO 50001 vs ESOS question: they are not competing regimes — a certified ISO 50001 energy management system deems compliance for any part of your energy consumption that falls under it, and where all of your total or significant energy consumption falls under it, no lead assessor review is required.
The completed ESOS assessment must be reviewed by a lead assessor before the responsible undertaking submits its ESOS notification to the Environment Agency, which regulates ESOS in England and can inspect evidence packs or open compliance investigations.
The full step-by-step walkthrough is in the dedicated ESOS compliance guide; for external support and tooling, see choosing ESOS consultants and assessors and managing ESOS online. Templates are in ESOS templates.
The ESOS regulators, by nation
The Environment Agency is the scheme administrator for the UK, but each nation has its own compliance body.
ESOS, SECR and UK SRS S2
ESOS energy-audit data does not replace other reporting duties — it feeds directly into them.
ESOS sits alongside two other UK reporting regimes that many qualifying organisations also face.
SECR (Streamlined Energy and Carbon Reporting) requires annual energy-use and emissions disclosure in the directors’ report for large companies and LLPs — a different obligation to ESOS’s four-yearly audit cycle, but drawing on the same underlying energy data. The two regimes are compared line by line in ESOS vs SECR.
Looking further ahead, UK SRS S2 climate disclosures will require in-scope listed companies to report Scope 1 and 2 emissions calculated from actual energy consumption, and ESOS audit data is a natural evidence source for that calculation — see the GOV.UK UK SRS guidance for the disclosure framework.
See how ESOS energy data feeds into UK SRS S2 for the practical mapping between the two.
ESOS — frequently asked questions
ESOS is the Energy Savings Opportunity Scheme — the UK’s mandatory energy-audit scheme for large undertakings, established by SI 2014/1643 and administered by the Environment Agency. Qualifying organisations must audit at least 95% of their energy consumption once every four years and notify the regulator.
ESOS stands for the Energy Savings Opportunity Scheme — a UK government mandatory energy-audit scheme for large organisations. Qualifying businesses must measure their total energy use and have it audited by a registered lead assessor at least once every four years.
Any UK large undertaking qualifies: an organisation with 250 or more employees, or one with more than £44m turnover and more than £38m on its balance sheet. Corporate groups qualify if the group meets the thresholds overall, and qualifying overseas-owned UK subsidiaries are also in scope. See ESOS exemptions for who is excluded.
ESOS began in 2014 as the UK’s implementation of Article 8 of the EU Energy Efficiency Directive, but that is no longer its legal basis — the scheme now rests on the Energy Act 2023, sections 254 to 260 and 263. It is designed to surface cost-effective energy-saving opportunities in large organisations, supporting national energy-efficiency and net-zero goals, and is enforced by the Environment Agency with civil penalties for non-compliance.
The Phase 4 qualification date is 31 December 2026, and the compliance notification deadline is 5 December 2027. Organisations must submit their notification to the Environment Agency via the MESOS portal by that date.
The Environment Agency can issue a civil penalty of up to £5,000 for failing to notify by the deadline, plus £500 per working day (up to a further £40,000, capped at 80 working days) for continued non-compliance. Failing to undertake the ESOS assessment at all carries a higher initial penalty of up to £50,000, and separate penalties apply for false statements or inadequate evidence packs.
Yes. ESOS is a statutory obligation under the Energy Savings Opportunity Scheme Regulations 2014 (SI 2014/1643), as amended in 2023 and 2026. It is not voluntary for organisations that meet the qualification test.
31 December 2026. GOV.UK states it directly: “The qualification date for the fourth compliance period is 31 December 2026.” Your corporate structure and financial position on that single day determine whether you are in scope.
A period of 12 consecutive months over which you calculate total energy consumption. For Phase 4 it must include the qualification date of 31 December 2026 and end on or before the compliance date of 5 December 2027 — so it begins between 1 January and 6 December 2026.
At least 95% of total energy consumption. Up to 5% may be excluded as “de minimis” energy consumption, and what you exclude must be recorded in your evidence pack. The threshold was 90% before the 2023 Amendment Regulations.
No. SI 2026/701, in force 22 July 2026, removed Display Energy Certificates and Green Deal Assessments as alternative compliance routes for Phase 4. They can still supply data for energy intensity ratios, but they cannot substitute for an energy audit.
Not from the scheme, but from most of the work. Where all of your total energy consumption, or all of your significant energy consumption — the assets and activities accounting for not less than 95% of the total — falls under the certified system, you are deemed to have complied with the duty to appoint a lead assessor, carry out an audit and produce a report. You still notify.
Usually. You do not need one if you have zero energy consumption, use less than 40,000 kWh, or hold ISO 50001 certification under which all of your total — or all of your significant — energy consumption falls. All three still require a notification.
A Part 6A requirement introduced in 2023: after notifying, the responsible undertaking publishes what it intends to do about the opportunities the audit found, then reports annually against it. The Phase 4 action plan deadline is 5 December 2028.
Once in every four-year compliance period. Phase 4 runs from 6 December 2023 to 5 December 2027, and Phase 5 from 6 December 2027 to 5 December 2031.
Yes. ESOS is a UK-wide scheme. The Environment Agency administers it across the UK, with SEPA in Scotland, Natural Resources Wales in Wales and the NIEA in Northern Ireland acting as compliance bodies for organisations registered there.
Not in Phase 4. The proposals to refocus ESOS on net zero, and to realign the qualification thresholds with SECR, were both postponed to Phase 5. Any guidance describing Phase 4 as a net-zero scheme is describing something that has not been legislated.
ESOS glossary
A UK organisation meeting the 250-employee test or the combined £44m turnover / £38m balance-sheet test on the qualification date.
31 December 2026 — the single date on which corporate structure and financials are assessed against the ESOS thresholds for Phase 4.
An individual registered with an approved professional body who must review and sign off the ESOS assessment before notification. See the dedicated lead assessor guide.
The entity within a qualifying group that takes formal responsibility for compliance and submits the notification to the Environment Agency. By default, the highest UK parent.
The four-year cycle. Phase 4 runs 6 December 2023 to 5 December 2027.
The 12 consecutive months over which total energy consumption is calculated. Not the same thing as the compliance period.
The maximum 5% of total energy consumption that may be excluded from any audit or alternative compliance measure.
Regulation 25(2): those assets and activities which together account for not less than 95% of the participant’s total energy consumption, measured in energy measurement units or by energy spend. Identifying them is elective, and 95% is a floor, not a target.
The undertaking which has no parent, or only has parents which are overseas undertakings.
Energy consumed per unit of activity — per square metre, per unit of production, per person mile or tonne mile for transport.
The records supporting the assessment, held by the participant and produced on request. Not submitted with the notification.
“Manage your ESOS reporting” — the Environment Agency’s online notification system.
ESOS guidance — the official sources
Every figure on this page traces to one of these. Where GOV.UK links a source, we link it too; where it does not, we have added the primary document it summarises.
The official ESOS guidance is split across three GOV.UK documents — the scheme page, the Phase 4 publication of 30 July 2026, and the Phase 3 publication it was split from — plus the regulations themselves.
- Energy Savings Opportunity Scheme (ESOS): guidance — GOV.UK / Environment Agency
- How to comply with the Energy Savings Opportunity Scheme (ESOS) phase 4 — GOV.UK, published 30 July 2026
- The Energy Savings Opportunity Scheme Regulations 2014 (SI 2014/1643) — legislation.gov.uk
- The Energy Savings Opportunity Scheme (Amendment) Regulations 2023 (SI 2023/1182) — legislation.gov.uk
- The Energy Savings Opportunity Scheme (Amendment) Regulations 2026 (SI 2026/701) — made 23 June 2026, in force 22 July 2026
- SI 2026/701 — explanatory note — legislation.gov.uk
- Enforcement and sanctions policy, Annex 2: climate change schemes — civil penalties — Environment Agency
- The Energy Savings Opportunity Scheme Regulations 2014 — second Post Implementation Review — 18 July 2025 (PDF)
- Manage your ESOS reporting (MESOS) — GOV.UK service
- Complying with the Energy Savings Opportunity Scheme (ESOS): phase 3 — GOV.UK
- SI 2014/1643 regulation 4 — compliance periods and qualification dates
- SI 2014/1643 regulation 22 — the reference period
- SI 2014/1643 regulation 34A — the ESOS action plan
- ESOS phase 4, Appendix D: useful contacts and information — GOV.UK
- Energy Savings Opportunities Scheme — Scottish Environment Protection Agency
- Energy Savings Opportunity Scheme (ESOS) — Natural Resources Wales
- Energy Saving Opportunities Scheme (ESOS) — NetRegs, for Northern Ireland and Scotland
- PAS 51215-1:2025 — Energy and decarbonization assessment, Part 1: Process — BSI
- PAS 51215-2:2025 — Competencies of lead assessors and assessment teams — BSI
- PAS 51215:2014 — Competence of a lead energy assessor — BSI; remains the ESOS Phase 4 competency standard
- Association of Energy Engineers — ESOS register
- CIBSE Low Carbon Consultant register
- Elmhurst Energy Systems — find an assessor
- Energy Institute — ESOS
- Energy Managers Association — ESOS lead assessors
- Institute of Sustainability and Environmental Professionals — ESOS lead assessor register
- Quidos — ESOS register
- Climate change civil penalties — data.gov.uk
- Energy Savings Opportunity Scheme published data — data.gov.uk
- Strengthening the Energy Savings Opportunity Scheme (ESOS) — consultation and government response
- Appendix B — information to provide through the ESOS notification system (ODT)
- The UK Energy Efficiency Strategy — GOV.UK
- Energy Efficiency Directive, Article 8 — European Commission
- Energy audits and reporting research, including ESOS — Post Implementation Review 2020
- Department for Energy Security and Net Zero
- Environment Agency — the ESOS regulator in England
- Department for Business and Trade
- UK Sustainability Reporting Standards — GOV.UK / DBT
- Energy efficiency — GOV.UK topic
Verified against primary sources on 1 August 2026. SI 2026/701 came into force on 22 July 2026 and the GOV.UK Phase 4 guidance was published on 30 July 2026; both are reflected throughout this page.