ESOS Phase 4 rules are now law: the 2026 amendment regulations explained

Display Energy Certificates and Green Deal Assessments can no longer be used as alternative compliance routes. The Government's reasoning is that these instruments produce less detailed and less tailored recommendations than a proper ESOS energy audit.

For public-sector bodies and others who leaned on DECs to cover a portion of their energy consumption in Phase 3, this is a material change of plan. That consumption now needs to be covered by an ESOS-compliant energy audit, by ISO 50001 certification, or by another recognised route.

If your Phase 3 compliance involved DECs, treat that portion of your estate as unaudited for Phase 4 purposes and put it into your audit programme now. DECs remain valuable and, where required, legally necessary in their own right — they simply no longer discharge an ESOS obligation.

Organisations that were required to submit an ESOS Phase 3 action plan must now include an action plan review within the Phase 4 report and notification of compliance. This sits in addition to the annual progress updates already required in the two years following submission of the action plan.

Where commitments in the Phase 3 action plan have not been implemented — and are not expected to be implemented before the end of the Phase 4 compliance period — an explanation must be provided.

This is the single most significant cultural shift in the scheme. ESOS began as an audit-and-file exercise. It is now, in effect, an audit-and-account exercise. What you committed to in Phase 3 will be read back to you in Phase 4.

There is no penalty for a considered change of plan. Projects get superseded, sites get sold, better measures emerge. What matters is that the reasoning is documented and defensible rather than reconstructed from memory in late 2027.

Participants must now provide fuller information about the energy efficiency measures implemented during the compliance period. The report and notification must include details of the measures undertaken, an estimate of the energy savings achieved, and the energy saving category each measure relates to.

This matters for data collection. An estimate of savings achieved is not something you can generate retrospectively from an invoice folder. It needs a before-and-after basis: metered consumption, operating hours, or an engineering calculation recorded at the time the measure was installed.

The practical response is to start a simple measures register now — one row per intervention, with date, site, category, cost and the basis on which savings were estimated. Organisations that keep this live find Phase 4 reporting takes hours. Organisations that do not find it takes weeks.

The four-yearly cycle remains. Qualifying organisations must still carry out an assessment covering buildings, industrial processes and transport, and the assessment must still be reviewed and signed off by an approved ESOS Lead Assessor.

The compliance routes other than DECs and GDAs remain available: one or more ESOS energy audits, ISO 50001 certification covering the organisation's energy use, or a combination. Amendments have also been made relating to ISO 50001 participants and to regulator and professional body functions.

Net zero considerations can be included voluntarily in a Phase 4 assessment. This is optional, but for organisations with a public carbon commitment it is an efficient way to make one data-gathering exercise serve two purposes.

31 December 2026 — the qualification date for the fourth compliance period. Whether you are in scope is judged on your position on this date.

5 December 2027 — the compliance deadline for organisations that qualify.

Between the two sits the work: data collection, site audits, Lead Assessor review, action plan review, and board sign-off. Every phase to date has produced a rush of organisations appointing assessors in the final quarter, and a shortage of assessor availability when they do.

Confirm whether your corporate group qualifies on the 31 December 2026 qualification date, including overseas parents and UK subsidiaries. Group structure is the most common source of ESOS error — see our guide to ESOS qualification criteria.

Identify any consumption that was covered by DECs or Green Deal assessments in Phase 3 and reassign it to an audit route.

Retrieve your Phase 3 action plan and mark each commitment as delivered, in progress, superseded or abandoned, with a reason. Our article on ESOS action plans explains what good looks like.

Open a measures register covering the current compliance period and record savings estimates as measures are installed, not afterwards.

Appoint a Lead Assessor early. Our guidance on selecting an ESOS Lead Assessor sets out the questions worth asking.

Oak Tree Rule provides Lead Assessor support and end-to-end delivery through our ESOS service, and combines it with commercial energy audits where organisations want the recommendations to be genuinely investable rather than a compliance formality.

For multi-site estates, we usually run ESOS alongside TM44 inspections and EPC work so that one site visit programme feeds several obligations. See our article on ESOS for multi-site businesses.

This article summarises the position as at August 2026 and is general guidance, not legal advice. Your obligations depend on your group structure, energy consumption and the compliance routes you select.