ESOS · Requirements
ESOS requirements: every duty, sorted by who owes it
The ESOS requirements are set by the ESOS Regulations 2014 as amended in 2023 and 2026, and most of them fall on one entity: the responsible undertaking that complies for the group.
Directors, the lead assessor, other group members and the bodies that keep the assessor registers each carry requirements of their own.
Pick a role below to see its duties with the provision for each.
In one table
The ESOS requirements, one line each
The core requirements of Phase 4 in the order they fall.
The Phase 4 compliance guide reads each one against its regulation in detail.
| Requirement | Who | When | Provision |
|---|---|---|---|
| Test every UK group member against the size test | Responsible undertaking | On 31 Dec 2026 | Sch 1; reg 15 |
| Measure total UK energy consumption over a 12-month reference period | Responsible undertaking | Period ending by 5 Dec 2027 | reg 22 |
| Identify significant consumption, if chosen: at least 95% of the total | Responsible undertaking | With the calculation | reg 25 |
| Calculate an intensity ratio for each organisational purpose | Responsible undertaking | With the calculation | reg 25C |
| Audit the significant or total consumption, or rely on ISO 50001 | Responsible undertaking | Within the period | regs 26–27, 33 |
| Appoint a lead assessor and have the assessment reviewed | Responsible undertaking; lead assessor | Before notifying | reg 21 |
| Notify the assessor’s approval body of completion | Lead assessor | Within 7 days of the review result | reg 21(2A) |
| Produce the ESOS report, with savings achieved and the plan review | Responsible undertaking | Before 5 Dec 2027 | regs 27A, 27D, 27E |
| Confirm the assessment | One or two responsible officers | With the notification | regs 30, 31 |
| Notify compliance through MESOS | Responsible undertaking | By 5 Dec 2027 | reg 29 |
| Keep the evidence pack | Responsible undertaking | To at least 5 Dec 2035 | reg 28 |
| Notify the action plan | Responsible undertaking; officer confirms | By 5 Dec 2028 | reg 34A |
| Notify three progress updates | Responsible undertaking; officer confirms | By 5 Dec 2029, 2030, 2031 | reg 34B |
Whether an organisation is in at all is a separate question, worked through on the ESOS qualification page.
Who owes what
Requirements by role, with the provision for each
The Regulations name each actor and give each its own duties, so the clearest way to read them is by person.
The responsible undertaking is the relevant undertaking that complies for the participant: the highest parent by default, or another member chosen in writing.
It carries almost every duty, from the assessment to the last progress update.
Responsible officers are directors, or people exercising management control where there are no directors, and their role is to confirm.
The lead assessor reviews, and since 22 July 2026 also reports completion to their approval body.
Other group members comply inside the participant, with rights to information and choices if they leave.
The approval bodies, the Environment Agency and the other regulators have duties too, and those shape what a participant can ask of them.
Who owes what · SI 2014/1643
The relevant undertaking that complies for the participant: the highest parent by default, or another member chosen in writing (regs 18, 19; Sch 2).
- Carry out an ESOS assessment in the compliance periodreg 20Deemed done at zero kWh (reg 33A)
- Appoint at least one lead assessor, give them the previous evidence pack, and have the assessment reviewedreg 21(1)Not under 40,000 kWh (reg 21(3)); deemed under reg 33(3) or 33A
- Calculate total energy consumption over a 12-month reference period that begins no more than 12 months before the qualification date and ends by the compliance datereg 22(2), (5)
- If it chooses, identify the areas making up at least 95% of consumptionreg 25(1), (2)
- Calculate at least one energy intensity ratio for each organisational purpose with consumptionreg 25C
- Carry out an energy audit of the significant or total consumption, with representative site visitsregs 26, 27Not for what ISO 50001 covers (reg 33)
- Produce the ESOS report before the compliance datereg 27ANot required for Phase 4 on the reg 33(3) or 33A routes (reg 27A(2)(b))
- Estimate savings achieved in the period, in kWh, per measure and per purposereg 27DNot for a participant new to the scheme (reg 27D(3))
- Review the previous action plan: measures not implemented, and whyreg 27E
- Disclose the relevant parts of the report to each group undertakingreg 27C
- Keep an evidence pack for at least two further compliance periodsreg 28
- Notify compliance through the Notification System, after the qualification date and by the compliance datereg 29
- Produce and notify an action plan, then three progress updatesregs 34A, 34BNot at zero kWh (regs 34A(11), 34B(9))
- Tell the scheme administrator if it becomes aware of a breachreg 37(1)
- Answer a compliance notice from the regulatorreg 35
SI 2014/1643 as amended by SI 2023/1182 and SI 2026/701, read at legislation.gov.uk on 1 October 2026.
A map of duties, not advice on a particular case.
The duty holder
The duty stays with the undertaking
Every core ESOS requirement is written as a duty on the responsible undertaking, and none of it moves to an adviser.
The undertaking appoints the lead assessor, must give them the evidence pack from any previous assessment, and must ensure the assessment is reviewed, under regulation 21(1).
The Environment Agency’s Phase 4 guidance says the lead assessor will not be held responsible for compliance by the compliance bodies.
A consultant can do much of the work, but the notification is the undertaking’s, the confirmation is its directors’, and a penalty notice is served on it.
The undertaking must also tell the scheme administrator if it becomes aware it is in breach of any requirement, under regulation 37(1).
How the assessment is put together, step by step, is on the ESOS assessment page; buyers weighing outside help can read about the role of an ESOS consultant in the UK, or a separate account of ESOS consultants and consultancy audits.
Directors
One responsible officer or two, and what they confirm
A responsible officer is a director within section 250 of the Companies Act 2006 or, where the participant has none, a person exercising management control, under regulation 30(2).
One is enough where the lead assessor is independent of the participant; two are needed in any other case.
Independence is defined exhaustively: in the last 12 months the assessor must not have been an employee, a director, partner or person exercising management control, or a shareholder of the participant, or the spouse or civil partner of one.
The confirmation under regulation 31 covers scope, compliance with Parts 4 to 6, the accuracy of the notified information, and, since 22 July 2026, that the officer has seen and considered the audit recommendations and any certified energy management system relied on.
The action plan and each progress update carry a further confirmation by the responsible officer under regulations 34A(8) and 34B(7).
The independence test, and how to check an assessor against it, is on the ESOS lead assessor page.
| Case | Responsible officers | Provision |
|---|---|---|
| Lead assessor independent of the participant | 1 | reg 30(3) |
| Lead assessor not independent | 2 | reg 30(3) |
| No lead assessor: under 40,000 kWh | 2 | reg 30(3A) |
| Zero consumption | 2 | reg 30(3), residual limb |
Your route
Which requirements apply on your route
Four facts change the list of requirements: how much energy the participant uses, whether ISO 50001 covers it, how much it covers, and whether the lead assessor is independent.
Under 40,000 kWh, no lead assessor is needed, but every other requirement stays.
With ISO 50001 over all total or all significant consumption, the lead assessor, audit and ESOS report are deemed done, and the notification, action plan and updates remain.
At zero consumption, the assessment duties and the action plan are deemed done, and the notification remains.
Display Energy Certificates and Green Deal Assessments stopped being routes on 22 July 2026, though their data may still be used inside an assessment.
Your route, duty by duty · Phase 4
Total energy consumption over the reference period
ISO 50001 certification, valid on 5 December 2027
Is the lead assessor independent of the participant?
Not independent if, in the last 12 months, they were an employee, director, person exercising management control or shareholder, or the spouse or civil partner of one (reg 30(4)).
- Measure total energy consumption (the ESOS assessment, reg 20)Requiredreg 20; Part 4 Ch 2
- Appoint a lead assessorRequiredreg 21(1)
- Carry out an ESOS energy auditRequiredreg 26; Part 4 Ch 3
- Produce the ESOS reportRequiredreg 27A
- Keep an evidence packRequiredreg 28
- Notify compliance through MESOS by 5 December 2027Requiredreg 29(1)
- Responsible officers who confirm1reg 30(3)–(4)
- Action plan and three progress updatesRequiredregs 34A, 34B
SI 2014/1643 regs 20, 21, 26–30, 33, 33A and Part 6A, as amended by SI 2026/701.
An orientation aid, not advice.
How much
Coverage, data and site visits
All energy the participant consumes in the UK is measured, in kWh or by spend, over a reference period that begins no more than 12 months before the qualification date and ends by the compliance date.
The audit then covers either the total, or the areas the participant elects to identify as significant, which must together account for at least 95% of total consumption, measured in energy units or by spend.
The remainder, up to 5%, needs no audit, and the participant chooses what goes in it.
So far as reasonably practicable the audit rests on verifiable data over 12 months, under regulation 26(3), and where that is not available it may rest on a shorter period or a reasonable estimate, with the reasons recorded.
It must include visits to sites the undertaking considers representative of how energy is used, and the undertaking records how many sites there are, how many were visited and why those were chosen.
For Phase 4 the audit’s data must begin no earlier than 6 December 2022 and no more than 24 months before the audit starts; the windows are set out on the ESOS deadlines page.
Consequences
Which requirements carry a penalty
| Requirement breached | Maximum | Provision |
|---|---|---|
| Notify compliance | £5,000, plus up to £500 a working day for up to 80 working days | reg 43 |
| Keep records (the evidence pack) | £5,000, plus the cost of confirming compliance | reg 44 |
| Undertake an ESOS assessment | £50,000, plus up to £500 a working day for up to 80 working days | reg 45 |
| Comply with a compliance, enforcement or penalty notice | £5,000, plus up to £500 a working day for up to 80 working days | reg 46 |
| Not make a false or misleading statement | £50,000 | reg 47 |
| Action plan and progress updates | No penalty in Part 8; non-submission is published | regs 34A, 34B |
Each penalty also carries publication, naming the undertaking for at least a year.
The gap for action plans and updates is in the statute, not only in regulator policy, but an enforcement notice requiring one would be enforceable under regulation 46.
How a penalty is set in practice is on the ESOS penalties page.
Group members
What a group member is entitled to
Regulation 27C requires the responsible undertaking to disclose to each group undertaking the parts of the ESOS report that relate to it.
For an audit, those are the savings opportunities about its energy, assets or activities, their estimated costs and benefits, considerations for implementing them, and the analysis of its consumption.
Where the participant relied on deemed compliance, relevant parts of the evidence pack are disclosed too.
Where the law prohibits disclosure, the undertaking tells the scheme administrator which parts and why.
A member leaving the group before the compliance date may agree in writing to comply with its old group or its new one, or must comply on its own; the same choice runs for the action plan and updates under Schedule 2 paragraphs 7A and 7B.
Not in the Regulations
Requirements that do not exist
ESOS sets no energy reduction target and requires no measure to be implemented.
There is no ESOS certificate; the record of compliance is the notification and the published data.
There is no fee for notifying, the Environment Agency’s guidance says.
A net zero or decarbonisation assessment is voluntary: the GOV.UK ESOS page says participants may use PAS 51215-1 and -2:2025 for that, but PAS 51215:2014 remains the competence standard for lead assessors, and MESOS cannot receive a decarbonisation assessment.
ESOS is not an annual disclosure in the accounts; that is SECR, whose own requirements are on the SECR reporting guide, and whose size test is not the ESOS test, as the UK SRS thresholds page shows alongside the other statutory size tests.
Display Energy Certificates and Green Deal Assessments as compliance routes — omitted on 22 July 2026.
ISO 50001 must cover 100% of energy — Phase 4 accepts total or significant consumption.
Two progress updates — Phase 4 has three.
Estimates in “energy measurement units” — kWh since 22 July 2026.
Check yourself
Six statements about who owes what
Each answer names the provision it turns on.
The scheme’s structure — administrator, regulators and policy owner — is on the Energy Savings Opportunity Scheme page, and the instruments themselves on the ESOS legislation page.
The regulator’s documents are collected on the Environment Agency’s ESOS guidance collection and the GOV.UK ESOS page.
True or false?
01The lead assessor is legally responsible for the participant’s compliance.
02Two responsible officers confirm where no lead assessor was needed under 40,000 kWh.
03ESOS requires the measures in the action plan to be implemented.
04The 95% may be measured by energy spend.
05A group member is entitled to the parts of the ESOS report about its own energy.
06Failing to file an action plan carries a fixed fine.
6 statements.
Pick an answer to see the provision behind it.
Answers rest on the provisions named beside each one.
Nothing you pick is saved.
Frequently asked
ESOS requirements, answered
What are the ESOS requirements?
A qualifying participant must measure its total UK energy consumption over a 12-month reference period, have the significant part of it audited or covered by ISO 50001, have a lead assessor review the assessment unless an exemption applies, produce an ESOS report, have one or two responsible officers confirm it, notify the Environment Agency by the compliance date, keep an evidence pack, and then produce an action plan and annual progress updates.
The requirements are in the ESOS Regulations 2014 as amended in 2023 and 2026.
Who is responsible for ESOS compliance?
The responsible undertaking: the highest parent of the qualifying group by default, or another member chosen by written agreement.
It carries the duties to assess, appoint a lead assessor, produce the report, keep the evidence pack, notify, and produce the action plan and updates.
Directors confirm the work as responsible officers, and the lead assessor reviews it, but the duty stays with the undertaking.
Do directors have ESOS duties?
Yes, as responsible officers.
One or two are nominated under regulation 30, and the notification must include their confirmation that the participant is in scope, the undertaking has complied and the information is correct, and that they have seen and considered the audit recommendations and any certified energy management system relied on.
They also confirm the action plan and each progress update.
Is there an ESOS requirement to implement the recommendations?
No. ESOS requires an assessment, a notification, an action plan and progress updates, but no saving to be made and no measure to be implemented.
An action plan may state that no measure is proposed, though from Phase 4 the next report must review the last plan and explain any measure not implemented.
Which ESOS requirements carry a fine?
Five breaches in Part 8: failing to notify, failing to keep records, failing to undertake an assessment, failing to comply with a notice, and making a false or misleading statement.
No penalty attaches directly to the action plan or progress updates, though their non-submission is published and an enforcement notice requiring one would be enforceable.
What does the lead assessor have to do?
Review whether the ESOS assessment meets the Regulations and tell the responsible undertaking, and, since 22 July 2026, notify their own approval body within seven days that the assessment is complete, with two contacts for the undertaking, one of them the responsible officer.
The Environment Agency’s guidance says the lead assessor is not held responsible for the participant’s compliance.
What is the minimum coverage ESOS requires?
All of the participant’s UK energy is measured.
The audit then covers either total consumption or the areas the participant elects to identify as significant, which must account for at least 95% of total consumption, measured in energy units or by spend.
The rest, up to 5%, needs no audit.
Do group members have ESOS requirements of their own?
They comply as part of the participant, usually under the highest parent, and they are entitled to see the parts of the ESOS report about their own energy and assets.
If a member leaves the group, Schedule 2 lets it agree where it complies, or it complies on its own.
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 Regulations 2014 (SI 2014/1643)
Every requirement on this page, as amended.
- legislation.gov.ukSI 2014/1643, regulation 21 — the lead assessor
Appointment, review, the previous pack and the seven-day notice.
- legislation.gov.ukSI 2014/1643, regulation 26 — the energy audit
Coverage, verifiable data, site visits and the record of how the audit was done.
- legislation.gov.ukSI 2014/1643, regulation 27C — disclosure to group undertakings
What each group member is entitled to see.
- legislation.gov.ukSI 2014/1643, regulation 30 — responsible officers
Who may be one, and when one or two are needed.
- legislation.gov.ukSI 2014/1643, Part 8 — civil penalties
The five breaches that carry a penalty.
- legislation.gov.ukThe Energy Savings Opportunity Scheme (Amendment) Regulations 2023 (SI 2023/1182)
The report, ratios, action plans, updates and the 40,000 kWh limb.
- legislation.gov.ukThe Energy Savings Opportunity Scheme (Amendment) Regulations 2026 (SI 2026/701)
The Phase 4 requirements in force from 22 July 2026.
- Environment AgencyHow to comply with the Energy Savings Opportunity Scheme (ESOS) phase 4
The regulator’s reading, including what the lead assessor is not responsible for.
- Environment AgencyComply with the Energy Savings Opportunity Scheme (ESOS) — guidance collection
Where the Phase 3 guidance and its documents sit.
- GOV.UK (Environment Agency)Energy savings opportunity scheme (ESOS): find out if you qualify and how to comply
The approved registers, PAS 51215:2014 and the voluntary net zero assessment.
- Environment AgencyAnnex 2: Climate change schemes — civil penalties
How a penalty is set in practice.