ESOS Phase 4: the quiet deadline

What Phase 4 is, and who it catches

The Energy Savings Opportunity Scheme (ESOS) requires large UK undertakings to assess their energy consumption every four years and notify the Environment Agency^[1][3].

ESOS Phase 4 is the current cycle: the Phase 4 compliance period runs from 6 December 2023 to 5 December 2027, with qualification tested on 31 December 2026^[3].

What follows is our analysis of what changed and why it matters. If what you need is the compliance route itself — qualification, evidence, notification, action plan — the cluster reference for ESOS Phase 4 walks it end to end.

The rules are settled. SI 2026/701 was made on 23 June 2026 and came into force on 22 July 2026^[7], and the Environment Agency published its Phase 4 guidance on 30 July 2026^[3].

The qualification test is unchanged: an organisation is in scope if, on the qualification date, it employs 250 or more people, or has an annual turnover over £44 million together with an annual balance sheet total over £38 million^[1][3].

The Phase 4 guidance states that test in sterling^[3].

Corporate groups qualify together — if any UK group member meets the test, the whole UK group participates. Our sister site's breakdown of ESOS thresholds covers how that aggregation applies to part-year group changes.

SI 2026/701 did not touch those thresholds^[7]. Aligning them with SECR’s own sterling thresholds was proposed and then dropped: GOV.UK confirms the change “will not go ahead for Phase 4,” and no Phase 5 commitment to it has been published — only the introduction of net zero requirements has been deferred to Phase 5.

The timing subtlety most organisations miss in ESOS Phase 4: the assessment must draw on 12 consecutive months of energy data that include 31 December 2026 and end before 5 December 2027^[3].

Data collection for Phase 4, in other words, should already be running — an organisation starting its ESOS Phase 4 measurement in mid-2027 cannot retrofit a compliant evidence period.

This makes early preparation for Phase 4 essential.

ESOS Phase 4’s real changes — inherited from the 2023 reforms, now fully in force

The 2023 amendment regulations^[2] arrived mid-way through Phase 3, which meant their most demanding elements were softened by transition.

ESOS Phase 4 is the first full cycle in which they all bind from day one.

Phase 4’s own changes come from a different instrument: SI 2026/701^[7].

Coverage of 95% is a Phase 3 rule, not a Phase 4 one

ESOS Phase 4 assessments must cover at least 95% of total energy consumption across buildings, transport and industrial processes, leaving a de minimis of up to 5%^[3].

That is routinely written up as a Phase 4 change, and it is not — the rise from 90% to 95% came in with the 2023 amendment regulations and bound participants from Phase 3^[2].

The mechanical effect is that the “de minimis” bucket organisations used to exclude awkward-to-measure consumption — pool vehicles, small sites, sub-metered tenancies — is half what it was before Phase 3.

For multi-site estates it remains the single biggest driver of audit work in ESOS Phase 4.

Action plans, and a third progress update

Phase 3 introduced mandatory action plans; ESOS Phase 4 closes the loop.

The Phase 4 action plan is due by 5 December 2028 and covers 6 December 2027 to 5 December 2031^[3].

Progress updates follow on 5 December 2029, 5 December 2030 and 5 December 2031 — the third is new to Phase 4, added by regulation 28 of SI 2026/701^[8].

The ESOS assessment needs sign-off by one responsible officer where the lead assessor is independent of the participant, or two in any other case (SI 2014/1643 reg 30(2)–(4)) — described in Environment Agency guidance as sign-off by ‘director(s) or equivalent’. The action plan and each progress update must likewise be confirmed by the responsible officer, though the instrument does not state a one-or-two rule for those submissions. All three are submitted through the Notification System (MESOS)^[3].

There is no penalty for missing an action plan or a progress update: the Environment Agency guidance says regulators will not take enforcement action or issue a penalty for non-submission, and the Scheme Administrator publishes the failure instead^[3].

Three genuinely new duties

First, achieved-savings reporting: the ESOS report and the notification of compliance must state the energy savings achieved during the compliance period — the measures implemented, the saving from each measure in kWh, and each measure’s energy-saving category^[3].

Only the combined figure across all measures is published; per-measure savings are withheld as potentially commercially sensitive^[3].

Second, the action plan review: participants must identify the proposed measures from the previous action plan that were not implemented, and explain why^[3].

Those submissions are not published, though action plans and progress updates are^[3].

Third, the third progress update on 5 December 2031^[8].

Two routes, not four

Display Energy Certificates and Green Deal Assessments are no longer compliance routes: regulation 26 of SI 2026/701 omits regulation 34 of the 2014 Regulations^[7].

The Environment Agency’s stated reason is that they “provide more limited and less tailored recommendations than an ESOS energy audit”^[3].

DEC and GDA data can still feed an ESOS report — an intensity ratio, say — but it cannot substitute for the audit^[3].

That leaves two routes: a lead-assessor-reviewed ESOS energy audit, and ISO 50001^[5].

Where ISO 50001 certification covers total or significant energy consumption, the participant is deemed to have complied with the duties to appoint a lead assessor, carry out the audit and produce the ESOS report — a notification of compliance is still required^[3].

Partial certification exempts only the certified consumption; the remainder is audited under standard ESOS rules with a lead assessor appointed^[3].

No lead assessor is needed below 40,000 kWh of total consumption, and a participant with zero energy consumption needs no assessment at all — but still notifies^[3].

Our analysis: three things the deadline maths hides

The effective deadline is earlier than 5 December 2027.

Phase 3 demonstrated what happens when a large share of participants seek lead assessors in the final six months: capacity runs out and submissions slip.

The Environment Agency was forced into pragmatic late-notification arrangements in 2023–24.

Nothing in the ESOS Phase 4 design increases assessor supply, while the 95% rule increases assessment workload per participant.

Organisations beginning ESOS Phase 4 audits in 2026 buy themselves negotiating power on assessor fees; organisations starting in autumn 2027 will take whatever is left.

Early submission is now possible — and strategically useful.

Because the ESOS Phase 4 evidence period must include 31 December 2026, an organisation with audits complete can notify in early 2027, almost a year ahead of the deadline^[3].

For groups whose investors ask about energy governance under UK SRS S2^[6], a completed ESOS Phase 4notification is a concrete, citable data point rather than a promise.

ESOS data is UK SRS data.

The energy-consumption profile, the savings opportunities, and the action-plan delivery record that ESOS Phase 4 demands are precisely the inputs UK SRS S2 metrics and transition narratives require^[6].

Treating the ESOS audit as a one-off compliance artefact — the dominant Phase 1–3 pattern — now means paying twice for the same measurement.

The marginal cost of making ESOS Phase 4 outputs reporting-grade is small; the value in S2 preparation is not.

Organisations that want this handled end to end can engage a specialist ESOS consultancy.

For the step-by-step compliance route, see the ESOS Phase 4 compliance guide on our sister reference site.

ESOS Phase 4 — frequently asked questions