ESOS Phase 3 vs Phase 4 · the change map
ESOS Phase 3 vs Phase 4: what the 2026 Regulations changed
ESOS Phase 4’s changes come from one instrument, SI 2026/701, in force since 22 July 2026 — not from the 2023 amendments that shaped ESOS Phase 3.
It closed two routes, widened a third, added two items to the report and a third progress update.
It left the thresholds, the dates formula and the 95% line exactly where they were.
Two phases
Two cycles that overlap
Phase 3 ran from 6 December 2019 to 5 December 2023, but its compliance date was pushed back six months to 5 June 2024.
Phase 4 started on 6 December 2023 regardless, so the two overlapped from the start, and still do.
A Phase 3 participant owes its second progress update by 5 December 2026, weeks before its Phase 4 status is fixed on 31 December 2026, under Part 6A.
Qualifying for Phase 3 says nothing about Phase 4: the test is re-run on the new date, with the two-period status rule.
The Phase 4 test in detail is on ESOS Phase 4 thresholds.
| Phase 3 | Phase 4 | |
|---|---|---|
| Qualification date | 31 Dec 2022 | 31 Dec 2026 |
| Compliance period | 6 Dec 2019 – 5 Dec 2023 | 6 Dec 2023 – 5 Dec 2027 |
| Compliance date | 5 Jun 2024 (extended) | 5 Dec 2027 |
| Action plan | By 5 Dec 2024 | By 5 Dec 2028 |
| Progress updates | 5 Dec 2025, 5 Dec 2026 | 5 Dec 2029, 2030, 2031 |
| Changes made by | SI 2023/1182 | SI 2026/701 |
The change map
What SI 2026/701 changed, regulation by regulation
SI 2026/701 has 32 regulations.
These are the changes a participant will notice, with the regulation of SI 2026/701 that makes each.
| Area | Phase 4 rule | SI 2026/701 |
|---|---|---|
| DEC and Green Deal routes | Omitted — regulation 34 of the 2014 Regulations removed | SI 2026/701 reg 26 |
| ISO 50001 trigger | “Total or significant” consumption, and any part of consumption for partial cover | reg 24 (new reg 33(2A)) |
| ISO 50001 deeming | Now reaches the ESOS report (Chapters 3 and 3A) as well as the lead assessor and audit; no longer deems reg 20 | reg 24 (reg 33(3)) |
| Zero energy | New regulation 33A: no assessment, no lead assessor, no action plan — but still notify | reg 25 |
| Savings achieved | New regulation 27D: savings in the compliance period, in kWh, per measure and purpose | reg 17 |
| Action plan review | New regulation 27E: unimplemented measures and the reasons | reg 17 |
| Progress updates | A third, final update (reg 34B(1)(c)) | reg 28 |
| Units | kWh throughout estimates and plans | regs 13, 27, 28 |
| Lead assessor | Personal seven-day notification to the approval body (reg 21(2A)) | reg 8 |
| Estimates | Must be accompanied by the data used; methods and data into the evidence pack | regs 9, 18 |
| Insolvency | Excluded if in proceedings at any time from qualification date to compliance date | reg 6 |
| Publication | Combined savings published; Table G rows 2 and 4 now published; Table K (ISO route) not | reg 31 |
Three of the rows are genuinely new duties: savings achieved, the action plan review, and the third progress update.
One is a closure: regulation 26 omitted regulation 34, ending Display Energy Certificates and Green Deal assessments as routes.
Their data can still feed an intensity ratio or a past-savings estimate, but not replace an audit.
One is a widening: the Explanatory Note says ISO 50001 over total or significant consumption deems the duties to appoint a lead assessor, carry out an audit and produce a report — before, the certificate had to cover total consumption and the report was not deemed.
The rest is machinery: kWh throughout, data behind every estimate, and a personal duty on the lead assessor.
Unchanged
What Phase 4 left alone
SI 2026/701 amends many provisions but touches neither regulation 15 nor Schedule 1, so the qualification test is the one Phase 3 used.
It does not amend regulation 4 either, so no compliance date changed, whatever the Phase 4 guidance’s penalty section says about a revised deadline.
The four organisational purposes and the duty to give an intensity ratio for each are Phase 3 rules that continue.
The GOV.UK ESOS overview no longer carries the old statement that an alignment of the ESOS and SECR thresholds would not go ahead for Phase 4, and no instrument proposes one.
The size test: 250 persons, or over £44m and over £38m.
The dates formula in regulation 4.
The 95% significant-consumption line.
PAS 51215:2014 as the lead assessor competence standard.
Phase 3's changes
Changes often called Phase 4’s that were Phase 3’s
SI 2023/1182 came into force on 29 November 2023, in the middle of Phase 3.
Much of what is described as new in Phase 4 dates from it.
| Change | Made by | In force |
|---|---|---|
| Action plans and progress updates (Part 6A) | SI 2023/1182 reg 26 | 29 Nov 2023 |
| Significant consumption raised from 90% to 95% | SI 2023/1182 reg 13(b) | 29 Nov 2023 |
| No lead assessor below 40,000 kWh (reg 21(3)) | SI 2023/1182 reg 9 | 29 Nov 2023 |
| Site visits and the audit record (reg 26(3A), (9)) | SI 2023/1182 reg 16 | 29 Nov 2023 |
| Costs, benefits, payback and a programme in the audit (reg 27(1)(d)–(e)) | SI 2023/1182 reg 17 | 29 Nov 2023 |
| The ESOS report and energy intensity ratios | SI 2023/1182 | 29 Nov 2023 |
The 2023 Regulations are the reason a Phase 3 participant has already audited to the 95% line and already filed an action plan.
The government’s second post-implementation review lists them as the Phase 3 changes: a compliance report, an intensity ratio, a justified site sample, more information to the Environment Agency, and published action plans.
Describing them as Phase 4 changes hides what really is new, which is the savings-achieved figure and the review of the last plan.
What the audit now contains, clause by clause, is on ESOS energy audits.
ISO 50001
The ISO 50001 route got stronger
In Phase 3, an ISO 50001 certificate took the audit’s place only if it covered total energy consumption.
In Phase 4, a certificate covering all of the total or all of the significant consumption deems three duties: appointing a lead assessor, carrying out the audit and, newly, producing the report.
SI 2026/701 also removed the duty to carry out an ESOS assessment (regulation 20) from what the route deems; only the zero-energy route deems that.
Where it covers only part of the energy, it deems compliance for that part, and the rest is audited.
It never deems the notification, and it never removes the action plan that follows.
The route in full is on ISO 50001 and ESOS.
Reading the sources
Where the Phase 4 guidance disagrees with the law
The Environment Agency’s Phase 4 guidance, published on 30 July 2026, is the most useful practical document on ESOS, and it contradicts itself in places.
Where it and the Regulations part company, the Regulations govern, and a participant quoting the guidance against the instrument has no defence in that.
The GOV.UK ESOS overview was itself Phase 3 material until it was rewritten on 2 September 2026, and the earlier guidance collection still serves Phase 3.
The Phase 4 publication page is the one to bookmark, read with the instrument.
| Point | Guidance says | The Regulations say |
|---|---|---|
| Progress updates | Two (stages list, §14.3) and three (§14) | Three — reg 34B(1)(c) |
| Estimate units | “Energy measurement units” (§14.1) | kWh |
| Reference period end | “Before” the compliance date (§4.4) | “On or before” — reg 22(5) |
| Compliance date | Revised by the 2026 amendment (§15.1) | Reg 4 unamended |
| Sign-off | “Board level directors” | “Responsible officer” — reg 30(2) |
Net zero
Net zero: voluntary, and unsubmittable
SI 2026/701 contains no net zero requirement.
The GOV.UK ESOS overview says Phase 4 participants may voluntarily include net zero considerations, using PAS 51215-1:2025 for the process and PAS 51215-2:2025 for competencies.
It also says MESOS does not allow reporting of voluntary decarbonisation assessments, so a participant that does one publishes it through its own reports.
PAS 51215:2014 remains the competence standard for ESOS lead assessors.
For organisations reporting against UK SRS S2, a voluntary decarbonisation assessment can inform the transition disclosures; it does not discharge them.
In full
ESOS Phase 3 vs Phase 4, row by row
| Area | Phase 3 | Phase 4 |
|---|---|---|
| Qualification test | 250 persons, or > £44m and > £38m | Unchanged |
| Coverage | 95% (from 29 Nov 2023) | Unchanged |
| Routes | Audit, ISO 50001, DECs, Green Deal assessments | Audit or ISO 50001 only |
| ISO 50001 cover | Total consumption | Total or significant, or any part |
| Lead assessor exemptions | Under 40,000 kWh, or ISO 50001 over total consumption | Adds ISO 50001 over significant consumption, and zero energy |
| Lead assessor’s own duty | None | Notify the approval body within 7 days |
| ESOS report | Required | Adds savings achieved and the action plan review |
| Progress updates | Two | Three |
| Units for estimates | Energy measurement units | kWh |
| Insolvency exclusion | On the qualification date | Any time to the compliance date; SME members of an insolvent large undertaking too |
| Published data | Action plans and progress updates | Also the combined savings achieved |
| Net zero | Not part of ESOS | Voluntary; cannot be submitted |
Penalties did not change in amount; ESOS penalties sets out the table, and the one narrowing SI 2026/701 made to regulation 45.
The insolvency exclusion now reads “during the period beginning with the qualification date and ending with the compliance date”.
The sister reference’s ESOS Phase 4 compliance guide takes the same changes as a practical checklist, and the 2014 text itself is the revised ESOS Regulations.
Frequently asked
Phase 3 vs Phase 4: questions people ask
What changed between ESOS Phase 3 and Phase 4?
The ESOS (Amendment) Regulations 2026 (SI 2026/701), in force 22 July 2026, removed Display Energy Certificates and Green Deal assessments as routes; let ISO 50001 over total or significant consumption deem the lead assessor, audit and report duties; added reporting of energy savings achieved and a review of the last action plan to the ESOS report; added a third progress update; widened the insolvency exclusion; and gave the lead assessor a seven-day notification duty.
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, and its compliance date was extended to 5 June 2024.
Phase 4 began on 6 December 2023 regardless.
What is still due for ESOS Phase 3?
The second progress update on the Phase 3 action plan, by 5 December 2026.
The Phase 3 action plan itself was due by 5 December 2024 under regulation 34A(7)(a), and the Environment Agency accepted plans until 5 March 2025.
Did the ESOS thresholds change for Phase 4?
No. SI 2026/701 does not touch regulation 15 or Schedule 1, so the test remains at least 250 persons, or turnover in excess of £44 million and a balance sheet in excess of £38 million.
Was the 95% audit coverage new in Phase 4?
No. SI 2023/1182 raised the significant-consumption line from 90% to 95% from 29 November 2023, for Phase 3.
Phase 4 keeps it.
Is net zero part of ESOS Phase 4?
Not as a requirement.
SI 2026/701 contains no net zero duty.
The GOV.UK ESOS overview says Phase 4 participants may voluntarily include net zero considerations using PAS 51215-1:2025 and PAS 51215-2:2025, and that MESOS cannot receive such assessments.
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 2026 (SI 2026/701)
Made 23 June 2026, in force 22 July 2026: the Phase 4 changes. Made under Energy Act 2023 ss.254–260 and 263.
- legislation.gov.ukSI 2026/701, regulation 28 — the third progress update (new reg 34B(1)(c))
- legislation.gov.ukSI 2026/701, regulation 26 — omits regulation 34 (DECs and Green Deal assessments)
- legislation.gov.ukSI 2026/701 — Explanatory Note (with the correction slip applied)
ISO 50001 over total or significant consumption deems the lead assessor, audit and report duties.
- legislation.gov.ukThe Energy Savings Opportunity Scheme (Amendment) Regulations 2023 (SI 2023/1182)
In force 29 November 2023: Part 6A, the 95% line, reg 21(3), site visits, the reg 27 content.
- legislation.gov.ukThe Energy Savings Opportunity Scheme Regulations 2014 (SI 2014/1643), revised text
In force 17 July 2014. Consolidation of the 2026 amendments is partial — read with SI 2026/701.
- legislation.gov.ukESOS Regulations 2014, regulation 4 — compliance periods, qualification and compliance dates
The formula that generates 6 December 2023 – 5 December 2027, 31 December 2026 and 5 December 2027.
- legislation.gov.ukESOS Regulations 2014, Part 6A (regulations 34A–34B) — action plans and progress updates
Consolidated to 22 July 2026: contents, windows, kWh basis, the third progress update, the zero-energy carve-out.
- legislation.gov.ukESOS Regulations 2014, regulation 25 — significant energy consumption
90% until SI 2023/1182 reg 13(b) substituted 95% from 29 November 2023.
- legislation.gov.ukESOS Regulations 2014, regulation 16 — excluded undertakings
Public bodies (Procurement Act 2023 definition since 24 February 2025) and the insolvency exclusions widened on 22 July 2026.
- Environment AgencyHow to comply with the Energy Savings Opportunity Scheme (ESOS) phase 4
Published 30 July 2026. A restatement of the Regulations, never the source over them; where it and the SI differ, the SI governs.
- Environment AgencyComply with the Energy Savings Opportunity Scheme (ESOS) phase 4 — publication page
- Environment AgencyComply with the Energy Savings Opportunity Scheme (ESOS) — the earlier guidance collection
The Phase 3 material.
- Environment Agency / GOV.UKEnergy savings opportunity scheme (ESOS): find out if you qualify and how to comply
Rewritten for Phase 4 on 2 September 2026; seven approved lead assessor registers; PAS 51215-1 and -2:2025 voluntary.
- Department for Energy Security and Net ZeroThe ESOS Regulations 2014 — second Post Implementation Review (18 July 2025, PDF)
¶19: 9,871 groups believed to qualify for Phase 3; 8,581 notified; 5,403 action plans. Recommendation: keep.
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