The qualification date for the fourth phase of the Energy Savings Opportunity Scheme is 31 December 2026, fewer than 100 days away. Meet the thresholds on that date and you're required to comply, with your notification deadline following on 5 December 2027. Here's what you need to know, starting with the basics:
ESOS Phase 4 is mandatory if you meet at least one of the below tests, assessed as of 31 December 2026:
Employee count catches some organisations out as it includes everyone: full-time or part-time status makes no difference, and it includes owners, managers and partners.
If you are hovering close to the thresholds, use the two-year rule to assess qualification:
Qualification is assessed at the highest UK parent level, defined as the undertaking with no parent, or with parents that are all overseas. Once your UK parent qualifies, every UK subsidiary is automatically in scope, even one that wouldn't qualify on its own. There's no "too small to bother" opt-out at subsidiary level.
Normally, the highest UK parent acts as the responsible undertaking, responsible for ensuring the entire group complies with ESOS. Undertakings can disaggregate from that obligation, splitting into individual or smaller-group compliance rather than one consolidated report, but only with a written agreement signed by board directors (or equivalent) at every undertaking involved. It's not a shortcut: once disaggregated, each entity must comply on its own account, regardless of its individual size.
Qualified for Phase 3? Assume you still qualify unless your headcount or financials have shifted materially.
One nearer-term date if qualified for Phase 3: your further progress update (PU2) is due 5 December 2026, and the submission feature is now live on the MESOS portal. If you need help pulling together the measures implemented and savings achieved since your first update, contact us and we'll manage the submission for you.
Three changes matter most if you've done this before.
Display Energy Certificates and Green Deal Assessments no longer count as compliance routes. The Environment Agency's reasoning: they give more limited, less tailored recommendations than a full ESOS energy audit. If you relied on either previously, budget for a proper audit this time.
There's also a new action plan review requirement: as part of your Phase 4 assessment, you must look back at the action plan you filed for Phase 3, flag any measure you didn't implement and explain why. This sits inside your Phase 4 ESOS report and notification of compliance, separate from your own new Phase 4 action plan (due 5 December 2028), which then needs progress updates in 2029, 2030 and a newly added third round in 2031.
The ISO 50001 exemption also widened. Already ISO 50001 certified? Phase 4 treats you more generously than Phase 3 did. From Phase 4, the full exemption from appointing a lead assessor and producing a full ESOS report applies where your certified system covers all of your significant energy consumption, not just your total energy consumption as the old rule required, provided that certification falls within the Phase 4 compliance period (6 December 2023 to 5 December 2027) and is still valid on your 5 December 2027 compliance date.
Despite being in the proposed list of changes for Phase 4, a Net Zero or decarbonisation assessment is not mandatory under ESOS Phase 4. Government plans to make it compulsory have been pushed back to Phase 5.
Participants can choose to include a decarbonisation assessment using two new BSI standards: PAS 51215-1:2025 for the assessment process, and PAS 51215-2:2025 for assessor competency.
Compliance runs in stages, not a single deadline. Complete your ESOS audit and assessment, covering at least 95% of your total energy consumption through an audit, ISO 50001 or another compliance route, and notify the Environment Agency via MESOS by 5 December 2027. Submit your action plan by 5 December 2028, then file progress updates in 2029 and 2030, plus a third update, new for Phase 4, by 5 December 2031. Miss any one of these and you're non-compliant, not just the initial notification.
Penalties escalate fast: up to £5,000 for failing to notify, up to £50,000 for skipping the energy audit, plus up to £500 for every working day you stay non-compliant, capped at 80 days. Every breach is published on the Environment Agency's public register of non-compliant organisations, and for a large organisation, that reputational hit often outweighs the fine itself.
We manage your ESOS process end to end: scoping the audit, coordinating the energy assessment and preparing your notification, action plan and progress updates, so that no deadlines are missed.
The True platform does the modelling behind it: the ROI and carbon case for every measure in your action plan with savings tracked against your Phase 4 baseline. Your evidence and audit trail sit in one place, ready for the Environment Agency.
Recommending a measure is the easy part. We will take your action plan from paper to project, delivering the technology and tracking performance against the numbers we modelled, so ESOS becomes an investment case, not just a compliance exercise.
Not sure where you stand for Phase 4? Contact us to review your ESOS qualification before your 31 December 2026 qualification date. We'll confirm whether you qualify, what's changed for you specifically, and what to do next.
Want the full phase-by-phase detail? See our Complete Guide to ESOS.