Most businesses leave ESOS too late.
By the time the deadline comes around, assessors are booked, data is missing, and costs creep up.
Businesses that approach ESOS proactively usually come out the other side with stronger energy data, a clearer picture of where their costs sit, and a set of recommendations worth acting on. That’s the bit we want to help you get to.
What is ESOS Phase 4?
ESOS stands for the Energy Savings Opportunity Scheme. It’s a mandatory UK scheme run by the Environment Agency that requires large organisations to audit their energy use every four years. If you’re not sure whether your business qualifies or what’s involved, you can book a free ESOS consultation to talk it through.
Phase 4 is the current cycle. It started on 6 December 2023 and runs until 5 December 2027. Qualifying businesses need to measure energy use across buildings, transport and industrial processes, identify where they can cut consumption, and submit the results through the MESOS portal.
Does your business qualify for ESOS Phase 4?
Your business is in scope if, on 31 December 2026, it either employs 250 or more people, or has an annual turnover of more than £44 million and a balance sheet total of more than £38 million.
ESOS works on a “one in, all in” basis. If one UK entity in your corporate group qualifies, every UK entity needs to comply. Public sector organisations are exempt. Not-for-profits and charities are in scope if they meet the size thresholds.
The key dates for Phase 4
5 December 2027 is the big one. Your assessment needs to be signed off by a Lead Assessor and submitted to the Environment Agency by that date.
Before that, 31 December 2026 is your qualification date. Your energy data has to cover a 12-month period that includes it, so if you can start getting that data lined up in early 2026, the rest of the assessment becomes much less of a scramble later.
After compliance, you submit a Progress Update in December 2028 and another in December 2029, showing what you’ve done against your Action Plan.
What’s changed since Phase 3
A few things are worth knowing if you went through Phase 3.
Display Energy Certificates and Green Deal Assessments can’t be used as compliance routes anymore. Phase 4 requires a full ESOS-compliant audit.
Mandatory net zero reporting was originally due to land in Phase 4 but has been pushed back to Phase 5 (2027–2031). You can still opt in voluntarily now, and businesses that do will have a real head start when it becomes a requirement.
Qualification thresholds haven’t changed. If you qualified for Phase 3, you almost certainly qualify again.
How ESOS Phase 4 compliance works
There are three stages to Phase 4, and it helps to treat them as three connected jobs instead of one huge submission at the end.
Stage one is the ESOS assessment itself. You pull together 12 months of energy data, commission on-site energy audits on a representative sample of your sites, and cover transport and industrial processes too. Your ESOS Lead Assessor reviews the findings, signs them off, and submits everything through MESOS.
Stage two is the Action Plan. This is where you set out what you’re going to do about the findings: the energy-saving measures you’re putting in place, what you expect them to save, and how you’ll track it. A board-level director signs it off before it’s submitted.
Stage three is the annual Progress Update. You’ll need to submit updates in December 2028, December 2029 and December 2030 (dates to be confirmed by the Environment Agency), each showing what’s been implemented against your Action Plan. If your Action Plan is realistic, these are fairly quick to pull together.
Why starting early makes a difference
There’s a practical reason and a bigger-picture reason to start early.
The practical reason: site audits take time to schedule, energy data from landlords and suppliers is often slower to gather than expected, and Lead Assessors get booked up fast as the 2027 deadline approaches. Starting in 2026 gives you room to breathe on all of that.
The bigger-picture reason: ESOS gives you a thorough read on how your business actually uses energy, what it’s costing, and where the quick wins are. That insight feeds directly into carbon reduction plans, supplier conversations and your wider carbon footprint reporting. The work supports a lot of what you’re doing anyway.
How Planet Mark can help
Our ESOS Lead Assessors are authorised by the Environment Agency and have supported businesses through every phase of ESOS so far.
For Phase 4, we run the whole process end to end: the initial energy data review, on-site audits, fleet assessment, Board Summary Report and submission through MESOS. We stay on to help with the Action Plan and both Progress Updates, so the same team sees your compliance through to 2030.
The aim is to make ESOS worth the effort. You should come out of it with findings you trust, recommendations you can actually use, and savings you’re happy to put in front of the board.
Getting started
If your business looks likely to qualify for ESOS Phase 4, there’s no real benefit in waiting. Book a free ESOS consultation and we’ll talk through where you’re at and what a sensible next step looks like.
