ESOS Phase 3 · qualification 31 December 2022
ESOS Phase 3: what changed, and the filing still owed
ESOS Phase 3 ran from 6 December 2019 to 5 December 2023, and it is the phase that turned the scheme from a four-yearly audit into a cycle of plans and progress reports.
The changes came from SI 2023/1182, in force 29 November 2023, a week before the period ended.
Its compliance date has passed, but the Environment Agency’s Phase 3 guidance is plain: “The remaining deadline is to submit the second progress update report by 5 December 2026.”
ESOS Phase 3 changes
Ten changes SI 2023/1182 made
Each change is named to the provision it inserted or amended.
All of them carry into Phase 4; none of them is new in Phase 4.
| Change | Provision | Effect |
|---|---|---|
| Action plans after notification | Part 6A, reg 34A | A plan of the measures the participant proposes, with dates and estimated savings, or a nil statement |
| Annual progress updates | Part 6A, reg 34B | Two for Phase 3, each reporting against the plan |
| Significant consumption floor raised | reg 25(2), 90% → 95% | The de minimis residual fell from 10% to 5% |
| Calculating significant consumption | reg 25(3)–(4), inserted | Once elected, significant consumption must be calculated |
| Energy intensity ratios | Part 4 Chapter 2A | A ratio for each organisational purpose |
| The ESOS report | reg 27A | A written record of the assessment, kept in the evidence pack |
| Low-energy lead assessor exemption | reg 21(3), inserted | No lead assessor below 40,000 kWh of total consumption |
| Two officers where no assessor | reg 30(3A), inserted | Two responsible officers where reg 21(3) applies |
| A wider evidence pack | reg 28(1)(f)–(i), (2) | Report, notification, plan and updates kept for two further periods |
| Publication on a clock | reg 10(1)(c)–(e), (2) | Action plans and updates published within six months |
Phase 3 was also the first phase to qualify on the sterling thresholds: at least 250 persons, or turnover in excess of £44 million and a balance sheet total in excess of £38 million, replacing the euro figures used up to Phase 2.
The 2026 changes for Phase 4 — the end of Display Energy Certificate and Green Deal routes, the savings-achieved report, the action plan review and a third update — are on the Phase 4 compliance guide, and each phase’s changes side by side on ESOS phases.
Phase 2, 3 and 4 side by side
What Phase 3 changed, and what Phase 4 changed after it
The quickest way to see what Phase 3 did is to set it between the phase before and the phase after.
Against Phase 2, Phase 3 added almost everything that makes ESOS more than an audit: the report, the intensity ratios, the action plan and the progress updates.
It also tightened the existing machinery, raising the significant-consumption floor from 90% to 95% and switching the money limbs of the size test from euros to sterling.
Against Phase 4, Phase 3 still had four routes, an ISO 50001 route that only replaced the audit, two progress updates, and estimates in energy measurement units.
The comparison beside this text can be filtered by topic, or narrowed to what changed between Phase 3 and Phase 4.
What Phase 3 audits had to contain did not change much in Phase 4; what changed is what the Phase 4 report must say about the Phase 3 plan.
ESOS phase by phase
- Qualification date
- Phase 2
- 31 December 2018
- Phase 3
- 31 December 2022
- Phase 4
- 31 December 2026
- Compliance period
- Phase 2
- 6 Dec 2015 – 5 Dec 2019
- Phase 3
- 6 Dec 2019 – 5 Dec 2023
- Phase 4
- 6 Dec 2023 – 5 Dec 2027
- Notification of compliance by
- Phase 2
- 5 December 2019
- Phase 3
- 5 June 2024 (extended)
- Phase 4
- 5 December 2027
- Online system
- Phase 2
- Smart Survey
- Phase 3
- MESOS, from April 2024
- Phase 4
- MESOS
- Money limbs of the size test
- Phase 2
- Turnover over €50m and balance sheet over €43m
- Phase 3
- Turnover over £44m and balance sheet over £38m
- Phase 4
- Unchanged from Phase 3
- Employee limb
- Phase 2
- At least 250 persons
- Phase 3
- At least 250 persons
- Phase 4
- At least 250 persons
- Insolvency exclusion
- Phase 2
- Insolvency on the qualification date
- Phase 3
- Insolvency on the qualification date
- Phase 4
- Insolvency at any point from qualification to compliance date; wider group limb
- Compliance routes
- Phase 2
- Audit, ISO 50001, DECs, Green Deal Assessments
- Phase 3
- Audit, ISO 50001, DECs, Green Deal Assessments
- Phase 4
- Audit and ISO 50001 only
- ISO 50001 trigger
- Phase 2
- Total energy consumption
- Phase 3
- Total energy consumption
- Phase 4
- Total or significant energy consumption
- What ISO 50001 stands in for
- Phase 2
- The audit
- Phase 3
- The audit
- Phase 4
- The lead assessor, the audit and the ESOS report
- Lead assessor’s own notice
- Phase 2
- None
- Phase 3
- None
- Phase 4
- Notify the approval body within seven days
- Significant energy consumption
- Phase 2
- At least 90% of total
- Phase 3
- At least 95% of total
- Phase 4
- At least 95% of total
- Energy intensity ratios
- Phase 2
- None
- Phase 3
- One per organisational purpose
- Phase 4
- One per purpose, on verifiable data or a reasonable estimate
- ESOS report
- Phase 2
- Not required
- Phase 3
- Required
- Phase 4
- Required, with savings achieved and an action plan review
- Unit for estimates
- Phase 2
- Energy measurement units
- Phase 3
- Energy measurement units
- Phase 4
- kWh
- Savings achieved
- Phase 2
- —
- Phase 3
- Since the previous compliance date (reg 27B)
- Phase 4
- Per measure and per purpose, in kWh (reg 27D)
- Action plan
- Phase 2
- None
- Phase 3
- By 5 December 2024
- Phase 4
- By 5 December 2028
- Progress updates
- Phase 2
- None
- Phase 3
- Two: 2025 and 2026
- Phase 4
- Three: 2029, 2030 and 2031
- Review of the previous plan
- Phase 2
- None
- Phase 3
- None
- Phase 4
- Unimplemented measures and the reasons (reg 27E)
SI 2014/1643 as made and as amended by SI 2023/1182 (in force 29 November 2023) and SI 2026/701 (in force 22 July 2026); compliance dates from the Environment Agency’s period table.
The Phase 3 assessment
How a Phase 3 assessment was built
A Phase 3 participant tested its size on 31 December 2022 and measured its total energy consumption over twelve months that included that date.
It could then identify the areas making up at least 95% of the total, the new floor, and treat the rest as de minimis.
Those areas were covered by ESOS energy audits, by ISO 50001 certification over total consumption, or by Display Energy Certificates and Green Deal Assessments for the buildings they applied to.
For the first time the participant calculated an energy intensity ratio for each organisational purpose and recorded the assessment in an ESOS report under regulation 27A, which does not apply to any period ending on or before 5 December 2019.
A participant using less than 40,000 kWh no longer needed a lead assessor, but two responsible officers confirmed instead of one.
Notifications went through MESOS, which opened for registration on 19 March 2024 and for notifications on 30 April 2024, replacing the survey tool of the first two phases.
The compliance date was 5 June 2024 after the extension, and GOV.UK later asked anyone who had still not notified to do so by 6 August 2024.
ESOS Phase 3 dates
From the 2022 qualification date to December 2026
Phase 3 qualified on 31 December 2022 and its compliance period ran from 6 December 2019 to 5 December 2023, under regulation 4.
Its compliance date was extended by six months to 5 June 2024, the only time an ESOS compliance date has moved.
The extension did not move the plan: action plan and update windows run from the first day of the next compliance period, 6 December 2023, under regulation 34A(10).
So the statutory action plan deadline was 5 December 2024 under regulation 34A(7)(a); the GOV.UK change note of 7 February 2025 said plans could still be submitted until 5 March 2025, an acceptance window rather than a statutory date.
The plan covers 6 December 2023 to 5 December 2027, which is exactly Phase 4’s compliance period.
The first progress update was due by 5 December 2025 and the second is due by 5 December 2026, twenty-six days before Phase 4 qualification on 31 December 2026.
The ESOS deadlines register sets these beside every other phase.
- 31 Dec 2022Qualification date
Size tested for Phase 3.
- 29 Nov 2023SI 2023/1182 in force
Part 6A and the other Phase 3 reforms.
- 5 Dec 2023Compliance period ends
Phase 4 begins the next day.
- 5 Jun 2024Compliance date (extended)
Notification of compliance.
- 5 Dec 2024Action plan
Statutory deadline; accepted until 5 March 2025.
- 5 Dec 2025Initial progress update
6 December 2024 to 5 December 2025.
- 5 Dec 2026Further progress update
6 December 2025 to 5 December 2026.
The filing still owed
The second progress update, due 5 December 2026
The duty follows the action plan: a participant that notified for Phase 3 and was required to produce a plan owes the update, whichever route it used for the assessment.
ISO 50001 is a route to compliance for the assessment, not an exemption from Part 6A.
The update covers 6 December 2025 to 5 December 2026 and measures from the notification of the first update, the “relevant event” in regulation 34B(8).
SI 2026/701 regulation 28 changed the unit of the estimate to kWh from 22 July 2026, so an update filed now reports in kWh, not “energy measurement units”.
A responsible officer confirms that they are satisfied the update complies and that they have seen and considered it (regulation 34B(7)), and it is notified through MESOS inside the reporting period.
The published Phase 3 data shows how the first round went: 1,453 of 7,062 organisations with a published plan, 20.6%, filed no first update, and 80.6% of dated updates arrived in the final 30 days.
The ESOS progress report page covers each limb, the three estimation methods and the four-year-versus-twelve-month error in the published filings.
Which measures in the latest action plan have been implemented since the last update, whether each met its planned date, and which have not.
An estimate of the reduction in energy consumption achieved, or to be achieved, in the reporting period, in kWh.
The method used for the estimate, from the three in reg 34B(4).
Source: reg 34B, as amended by SI 2026/701 reg 28
Who still has a Phase 3 obligation
The duty follows the plan, not the audit route
A participant that notified compliance for Phase 3 and was required to submit an action plan owes the second progress update.
That includes participants that used ISO 50001, Display Energy Certificates or Green Deal Assessments instead of an energy audit, because the plan and the updates are separate duties from the assessment.
It includes participants whose plan said no measures were proposed: the guidance says the update requirement applies even then.
It does not depend on the participant’s size today, because Phase 3 status was settled on 31 December 2022.
An undertaking that has left the group since the plan was filed still owes the update, and the guidance lets it comply with its old group, its new one, or on its own.
Anyone unsure whether a plan was filed can check the Environment Agency’s published action-plan data, and the GOV.UK ESOS page asks anyone who never submitted a Phase 3 plan to contact the Agency.
Draft the 5 December 2026 update
Build the update measure by measure
The builder beside this text lays out what regulation 34B(3) asks for, one row per measure in the Phase 3 plan.
For the further update the reporting period is 6 December 2025 to 5 December 2026, and the savings figure is for those twelve months only.
It covers measures implemented since the first update was notified, says whether each met the date the plan gave, and lists the plan’s measures that have not been implemented.
The guidance lets an update include measures that were not in the original plan, with their own estimates and methods.
It also says the update is owed even where the plan stated that no measures were proposed.
The Environment Agency recommends filing near the deadline, so that the savings reported cover as much of the year as possible and rest on actual data rather than estimates.
Regulation 34B(3) · one row per measure in the plan
Relevant reporting period 6 December 2025 – 5 December 2026 (reg 34B(1)(b)).
The update is notified within that window, and the kWh figure is for that period, not for the plan’s four years.
1 implemented (0 after the plan’s date) · 0 not implemented · 0 kWh in the period
A responsible officer confirms the update and that they have seen and considered it (reg 34B(7)); it is filed through MESOS and published.
Fields follow SI 2014/1643 reg 34B(3)–(5) as amended by SI 2026/701 reg 28.
A working aid, not the MESOS form; nothing is saved.
Three ways to produce the number
The estimate, and the method behind it
Every saving in a progress update needs a method, and regulation 34B(4) allows three.
The Environment Agency’s guidance adds that the update does not have to separate savings already achieved from savings expected in the period; a pro-rata of actual savings is acceptable if the method is given.
Its examples of a reasonable method include comparing meter data before and after a measure, using the rated power of replaced equipment, and validating a feasibility-study estimate after installation.
The method choice matters in the published data: an action-plan figure carried over without rescaling is the source of the commonest error in Phase 3 updates.
Whatever the method, the calculation and its data go into the evidence pack.
| Method | Provision | What it needs |
|---|---|---|
| The estimate from the energy audit | reg 34B(4)(a) | The audit’s saving for that measure, scaled to the twelve months |
| The estimate in the action plan | reg 34B(4)(b) | The plan’s figure, converted from the plan’s period to the twelve months |
| Another reasonable estimation method | reg 34B(4)(c) | A description of the method and the reason for using it, in the evidence pack (reg 34B(5)) |
What the published record shows
How the first Phase 3 update actually went
The Environment Agency publishes every action plan and progress update, and its Phase 3 dataset lets the first round of updates be read directly.
Of 7,062 published action plans, 5,609 were followed by a first progress update, so 1,453 organisations filed a plan and then nothing.
Of 5,549 updates with a readable submission date, 4,474 arrived in the final 30 days and 624 after the 5 December 2025 deadline.
Across 30,481 measure rows in 5,054 updates, 7,301 measures, 24.0%, were marked implemented, and 896 of those went in later than the date the filer’s own plan had set.
Of 3,011 implemented measures whose estimate came from the action plan, 436 reported the plan’s four-year total unchanged as the twelve-month figure, and 124 reported more saving in twelve months than their whole four-year plan.
The median ratio of the twelve-month figure to the plan’s four-year total was 0.250, which is what dividing by four looks like.
One caution in reading the file: the estimation-method column is blank on about half the rows, and the blanks track the rows marked not implemented, so method counts must use the implemented rows only.
The 2025 post-implementation review adds the scheme-level view: 9,871 groups believed to qualify, 8,581 notifications and 5,403 action plans, of which 4,716 included at least one energy saving action, on data it describes as provisional.
What the figures are, and are not
Counted, not alleged
Every figure in the section above is computed from the Environment Agency’s own published workbooks; none is modelled or sampled.
A figure such as “436 reported the four-year total” establishes that a published number equals the plan’s number, not why, and a filer may have a reason the data cannot show.
The 1,453 organisations with no first update include any that became insolvent, restructured or had a reason the dataset does not record.
The dataset covers the first update only; the second, due on 5 December 2026, has not yet been filed or published.
Nothing here names or characterises any organisation, and the published files are the place to look up a particular filer.
Sign-off and filing
A director has to see it, and say so
Regulation 34B(7) requires the notification to confirm that the responsible officer is satisfied the update complies and has seen and considered it.
That is a personal act by the officer, which is why it is the step that most often makes a filing late: it depends on someone else’s calendar.
The Regulations speak of “the responsible officer” here without fixing whether one or two must confirm, and the guidance says a director or directors; where the number matters, ask the Environment Agency before filing.
The update is notified through MESOS within the relevant reporting period, which for this update ends on 5 December 2026 (regulation 34B(6)).
A lead assessor is not needed for a progress update, but if one helps, the seven approved registers on the GOV.UK page are the check, and membership of a body is not the same as being on its ESOS register.
Publication
Published, on a six-month clock
Publication is not discretionary: regulation 10(2) requires each progress update to be published within six months of its deadline or of its filing, whichever is later.
An update filed by 5 December 2026 should therefore appear in the public data by early June 2027, which matches the lag the Phase 3 dataset already shows.
What is published is decided field by field by Schedule 3, so it is worth reading before writing anything you would not want quoted.
This filing falls under the Phase 3 rules, and the existing Phase 3 dataset is an accurate guide to how it will look.
Phase 4 filings will look different, because SI 2026/701 regulation 31 rewrote Schedule 3 for them.
Two deadlines, one December
Twenty-six days between two phases
December 2026 carries two ESOS dates that belong to different compliance periods: the Phase 3 update on 5 December and the Phase 4 qualification date on 31 December.
They pull in opposite directions: the update looks back at measures committed to in 2024, while qualification looks at the size of the business in the financial year ending on or before the end of the month.
The Phase 4 test is unchanged from Phase 3: at least 250 persons, or turnover in excess of £44 million together with a balance sheet total in excess of £38 million.
A caution for anyone reading the Phase 4 guidance for this update: its section 14.1 gives “6 December 2025 to 5 December 2026” as the window for the second Phase 4 update, which is in fact the Phase 3 window.
That window is right for this filing and wrong for the Phase 4 update the section is describing; the guidance’s own worked example in section 14.2.3 gives 6 December 2029 to 5 December 2030.
After December
The Phase 4 calendar that follows
Once this update is in, Phase 3’s listed duties are done and the calendar belongs to Phase 4.
Phase 4 qualifies on 31 December 2026, notifies by 5 December 2027 and files its action plan by 5 December 2028, covering 6 December 2027 to 5 December 2031.
Three progress updates follow, by 5 December 2029, 2030 and 2031, the third inserted by SI 2026/701.
Two Phase 4 changes reach back into this filing: the Phase 4 report must estimate the savings achieved since 6 December 2023, and it must explain every Phase 3 plan measure not implemented.
What is reported in December 2026 is therefore what will be explained in December 2027.
Before 5 December 2026
Six steps, in the order that works
| Step | What to do | Why |
|---|---|---|
| 1 | Find the notified Phase 3 plan and the first update as filed | The update reports against the plan as notified, from the first update onwards |
| 2 | List what was implemented since the first update, with dates | Regulation 34B(3)(a) asks whether each met the plan’s date |
| 3 | Estimate each saving for 6 Dec 2025 – 5 Dec 2026 only, in kWh | The period is twelve months, and the unit changed in July 2026 |
| 4 | Name the method for each estimate; record any “other” method | Regulation 34B(4)–(5) |
| 5 | Get a responsible officer to see, consider and confirm it | Regulation 34B(7) |
| 6 | Notify through MESOS before 5 December 2026, and file the working | The update is published; the working goes in the evidence pack |
Step 2 is also the first draft of the Phase 4 action plan review: every measure that has not been implemented, and will not be by 5 December 2027, will need a reason in the Phase 4 report.
Seven things repeated about Phase 3
True or false, with the provision
Phase 3 attracts its own set of errors, mostly from summaries written before its last duty was clear or before SI 2026/701 changed the unit.
The most expensive is the belief that Phase 3 is closed, because it leads straight to a missed update that the Phase 4 report then has to explain.
The most common in the published data is the twelve-month figure that is really a four-year one.
Each answer beside this text names the provision or guidance passage that settles it.
Phase 3 · true or false?
01Phase 3 is over.
02The six-month extension also pushed back the Phase 3 action plan.
03A Phase 3 plan that proposed no measures needs no progress update.
04The 95% floor and action plans arrived in Phase 4.
05The second Phase 3 update is reported in kWh.
06Missing the second Phase 3 update carries a fine.
07A twelve-month progress figure can simply repeat the plan’s four-year estimate.
7 statements.
Pick an answer to see the provision behind it.
Answers rest on the provisions named beside each one.
Nothing you pick is saved.
If it is missed
No penalty, but a public record and a Phase 4 review
Part 8 of the Regulations attaches no penalty to action plans or progress updates, and the Environment Agency says regulators will not take enforcement action for their non-submission.
The penalty that does exist in Phase 3 attaches to the notification: regulation 43 sets up to £5,000 plus £500 a working day, capped at 80 working days, for failing to notify.
Regulation 10 makes the Environment Agency publish every action plan and progress update within six months of its deadline or its filing, whichever is later, so a missing update is visible beside every organisation that filed.
A Phase 3 participant that is large again on 31 December 2026 must, in its Phase 4 ESOS report, identify the measures in this plan that have not been and will not be implemented, and explain why (regulation 27E).
What is published in Phase 4 changes too: SI 2026/701 regulation 31 rewrote Schedule 3, so the Phase 3 data is no guide to Phase 4 disclosure.
The ESOS penalties page covers enforcement, and ESOS action plan the plan and its Phase 4 review.
What Phase 3 hands on
From Phase 3 to Phase 4 and beyond
Phase 4 qualifies on 31 December 2026 and notifies by 5 December 2027, and its test is unchanged from Phase 3.
Qualification is read from the accounts for the year ending on or in the 12 months before 31 December 2026, and an undertaking that was large keeps that status until it has been below the test for two consecutive accounting periods; see ESOS qualification and ESOS exemptions.
Everything SI 2023/1182 added carries forward: the 95% floor, the ratios, the ESOS report, the lead assessor exemption and the plan-and-update cycle, which for Phase 4 gains a third update due by 5 December 2031.
The Phase 4 assessment, audit and report are on the ESOS assessment, ESOS energy audit and ESOS reporting pages, with working structures on ESOS templates.
The notification is covered on ESOS notification, the lead assessor on ESOS lead assessor, and the next period on ESOS Phase 5.
The instruments are on ESOS legislation and the regulations, read one by one; the official documents compared on ESOS compliance guidance; and the scheme as a whole on the Energy Savings Opportunity Scheme.
What ESOS is not
Neighbouring regimes and who regulates
SECR is annual energy and carbon disclosure in the directors’ report; ESOS is a four-yearly assessment notified to a regulator.
See SECR and ESOS and SECR.
A Carbon Reduction Plan for major central government contracts, required by procurement policy under PPN 006, is a different document from an ESOS progress update, and neither discharges the other.
ISO 50001 certification relied on for ESOS must come from a body accredited by UKAS, an EU national accreditation body or a member of the International Accreditation Forum; see ISO 50001 and ESOS and UKAS accreditation.
An ESOS audit and a director’s sign-off are not third-party assurance; sustainability assurance explains what an assurance engagement is.
ESOS is UK-wide: the Environment Agency administers it for the whole UK, and the regulator follows the registered office — the Environment Agency, Natural Resources Wales, SEPA or the Northern Ireland Environment Agency — with the Secretary of State for DESNZ for activities wholly or mainly offshore.
The UK sustainability regulation timeline places ESOS among the other regimes.
The record
ESOS Phase 3 key facts
| Fact | Value | Source |
|---|---|---|
| Compliance period | 6 December 2019 to 5 December 2023 | reg 4(2) |
| Qualification date | 31 December 2022 | reg 4(3) |
| Notification of compliance | 5 June 2024, extended from 5 December 2023 | EA compliance-period table |
| Late notifications asked for by | 6 August 2024 | GOV.UK update log, 8 July 2024 |
| Size test | At least 250 persons, or turnover over £44m and balance sheet over £38m | Sch 1 ¶¶1, 1A |
| Significant consumption floor | 95%, up from 90% | reg 25(2); SI 2023/1182 |
| Routes | Audit, ISO 50001 over total consumption, DECs, Green Deal Assessments | reg 26 (before 22 July 2026) |
| Action plan | 5 December 2024; accepted until 5 March 2025 | reg 34A(7)(a); GOV.UK |
| Plan covers | 6 December 2023 to 5 December 2027 | reg 34A(10) |
| Initial progress update | 5 December 2025 | reg 34B(1)(a) |
| Further progress update | 5 December 2026, in kWh | reg 34B(1)(b); SI 2026/701 reg 28 |
| Penalty for a missed plan or update | None; the failure is published | Part 8 |
| Groups believed to qualify | 9,871 (provisional) | PIR 2025 ¶19 |
| Notifications | 8,581, 87% of that estimate (provisional) | PIR 2025 ¶19 |
The library
Documents behind this page
The instruments
- legislation.gov.ukSI 2014/1643 — table of contents
- legislation.gov.ukRegulation 27 — the energy audit
- legislation.gov.ukRegulation 33A — zero energy consumption (2026)
- legislation.gov.ukSchedule 3 — what is published
- legislation.gov.ukSI 2026/701 — as made
- legislation.gov.ukSI 2026/701, regulation 6 — insolvency exclusion widened
- legislation.gov.ukSI 2026/701, regulation 31 — Schedule 3 rewritten for Phase 4
The regulators and the data
- Environment AgencyComply with ESOS phase 3 — publication page
- GOV.UKEnvironment Agency
- GOV.UKDepartment for Energy Security and Net Zero
- Natural Resources WalesNatural Resources Wales — home
- SEPAScottish Environment Protection Agency — home
- DAERANorthern Ireland Environment Agency
- data.gov.ukdata.gov.uk — the government’s open data catalogue
- Companies HouseFind and update company information
Neighbouring regimes and standards
Four of the seven approved lead assessor register bodies
- Association of Energy EngineersAEE
- CIBSECIBSE
- Elmhurst EnergyElmhurst Energy
- Energy InstituteEnergy Institute
- Energy Managers AssociationEMA
- ISEPInstitute of Sustainability and Environmental Professionals
- QuidosQuidos
The seven approved registers are listed on the GOV.UK ESOS page, and membership of a body is not the same as being on its ESOS register.
This site is an independent reference; see the privacy policy and terms of service.
Frequently asked
ESOS Phase 3, answered
What changed in ESOS Phase 3?
The Energy Savings Opportunity Scheme (Amendment) Regulations 2023, SI 2023/1182, in force 29 November 2023, added action plans and annual progress updates (Part 6A), raised the significant energy consumption floor from 90% to 95%, introduced energy intensity ratios for each organisational purpose and the ESOS report, exempted participants using less than 40,000 kWh from appointing a lead assessor (with two responsible officers instead), and required the Environment Agency to publish action plans and progress updates within six months.
What was the ESOS Phase 3 deadline?
The compliance date for Phase 3 was extended by six months to 5 June 2024.
The action plan was due by 5 December 2024, and the Environment Agency accepted plans until 5 March 2025.
Two progress updates follow, due by 5 December 2025 and 5 December 2026.
What was the ESOS Phase 3 qualification date?
31 December 2022.
The Phase 3 compliance period ran from 6 December 2019 to 5 December 2023.
Is ESOS Phase 3 finished?
No. The Environment Agency’s Phase 3 guidance, updated 30 July 2026, says the remaining deadline is to submit the second progress update by 5 December 2026.
The update covers 6 December 2025 to 5 December 2026.
Did the Phase 3 extension move the action plan dates?
No. The six-month extension moved the Phase 3 compliance date to 5 June 2024.
The action plan and progress update dates run from the start of the next compliance period, 6 December 2023, under regulations 34A(10) and 34B, so they stayed at 5 December 2024, 2025 and 2026.
Does ISO 50001 exempt us from the Phase 3 progress update?
No. ISO 50001 is a route to compliance for the assessment, not an exemption from Part 6A.
A participant that notified and was required to produce an action plan owes the progress updates whichever route it used.
Is there a fine for missing the Phase 3 progress update?
No. Part 8 of the Regulations attaches no penalty to action plans or progress updates, and the Environment Agency’s guidance says regulators will not take enforcement action for their non-submission.
The failure is published.
The Phase 4 report will also have to review the Phase 3 plan measure by measure.
Who regulates ESOS offshore?
The Secretary of State for Energy Security and Net Zero, where an organisation’s activities are wholly or mainly offshore.
Onshore, the regulator follows the registered office: the Environment Agency, Natural Resources Wales, SEPA or the Northern Ireland Environment Agency.
What did ESOS Phase 3 require?
A qualifying group measured its total energy consumption over a 12-month reference period including 31 December 2022, covered its total consumption, or the at least 95% it identified as significant, with energy audits, ISO 50001, Display Energy Certificates or Green Deal Assessments, calculated an energy intensity ratio for each organisational purpose, wrote an ESOS report, had a lead assessor review it unless exempt, notified compliance by the extended date of 5 June 2024, and then filed an action plan and two progress updates.
Were Display Energy Certificates allowed in ESOS Phase 3?
Yes.
Display Energy Certificates and Green Deal Assessments were still compliance routes in Phase 3.
SI 2026/701 removed them from 22 July 2026, so they are not routes for Phase 4, although their data can still be used inside an assessment.
How many organisations complied with ESOS Phase 3?
The 2025 post-implementation review records that the Environment Agency believed 9,871 corporate groups qualified for Phase 3, and that on data published in February 2025 8,581 had notified, 87% of that estimate, of which 7,145 confirmed they were required to comply.
5,403 notifying groups had submitted an action plan.
The review says the data is provisional.
How many progress updates are there for Phase 3?
The Environment Agency lists two: by 5 December 2025 and by 5 December 2026.
A third, final update was added to the Regulations by SI 2026/701 for compliance periods ending on or after 5 December 2027; no published source settles whether it reaches Phase 3 plans, and the Phase 3 guidance names 5 December 2026 as the remaining deadline.
Can a Phase 3 progress update include measures that were not in the plan?
Yes.
The Environment Agency’s guidance says an update reports measures taken against the action plan and may include measures that were not in the original plan, each with its estimated saving and method.
Sources
Primary sources
Every figure, date and status on this page traces to the instrument’s owner.
Secondary commentary is never the source for a number.
- legislation.gov.ukThe Energy Savings Opportunity Scheme (Amendment) Regulations 2023 (SI 2023/1182)
The Phase 3 reforms, in force 29 November 2023.
- legislation.gov.ukSI 2014/1643, Part 6A — action plans and progress updates
Inserted by SI 2023/1182; the source of the 2024–2026 Phase 3 dates.
- legislation.gov.ukSI 2014/1643, regulation 34A — the ESOS action plan
reg 34A(7)(a): Phase 3 plans due by 5 December 2024.
- legislation.gov.ukSI 2014/1643, regulation 34B — progress updates
What each update contains, how its estimate is made, who confirms it.
- legislation.gov.ukSI 2014/1643, regulation 4 — compliance periods
Phase 3: qualification 31 December 2022, period 6 December 2019 to 5 December 2023.
- legislation.gov.ukSI 2014/1643, regulation 10 — publication
Action plans and updates published within six months (reg 10(2), inserted 2023).
- legislation.gov.ukSI 2026/701, regulation 28 — progress updates amended
kWh for the estimate from 22 July 2026, and the final update for later periods.
- Environment AgencyComply with the Energy Savings Opportunity Scheme (ESOS): phase 3
Updated 30 July 2026: the remaining deadline is the second progress update, 5 December 2026.
- Environment AgencyHow to comply with the Energy Savings Opportunity Scheme (ESOS) phase 4
The compliance-period table with the Phase 3 extension; the action plan review.
- GOV.UK (Environment Agency)Energy savings opportunity scheme (ESOS): find out if you qualify and how to comply
The Phase 3 action plan acceptance window, and the reminder of the 5 December 2026 update.
- Environment Agency (data.gov.uk)Energy Savings Opportunity Scheme — published Phase 3 data
Action plans, first progress updates and notifications, 5 June 2026 data cut.
- legislation.gov.ukSI 2014/1643, regulation 43 — failure to notify
The penalty that does attach in Phase 3: the notification, not the plan.
- Department for Energy Security and Net ZeroThe ESOS Regulations 2014 — second post-implementation review (July 2025)
Phase 3 compliance data, provisional: groups believed to qualify, notifications, action plans.
- legislation.gov.ukSI 2014/1643, regulation 25 as originally made — the 90% floor
What SI 2023/1182 changed to 95% for Phase 3.