Most businesses think ESOS is finished once they’ve submitted a compliance notification. For anyone who qualified for Phase 3, it’s not. Two deadlines fall in the second half of 2026, within weeks of each other: the final Phase 3 progress update and the snapshot date that determines who is caught by Phase 4. This ESOS guide covers what both mean, when they land, and what to do before the year runs out.
Key Takeaways
- Phase 3 is not finished. The second and final annual progress update is due on the 5 December 2026, even though the original compliance notification deadline passed back in June 2024.
- Phase 4 qualification is assessed on 31 December 2026, based on your employee numbers, turnover and balance sheet on that date, not on when Phase 4 was announced.
- Businesses that have grown since 2022 may be newly in scope for Phase 4 even if they were never part of Phase 3.
- Non-compliance carries financial and reputational risk. Penalties can reach up to £50,000 for failing to notify or audit, plus daily fines for continued breaches, and non-compliant organisations are named on a public register.
- Wholesale gas prices remain volatile through 2026, driven by shipping risk around the Strait of Hormuz and gas storage running below seasonal norms. That makes the energy audit behind ESOS worth more than the compliance tick box.
Quick Answer: Is ESOS Still Relevant in 2026?
Yes. If your business qualified for ESOS Phase 3, you still have a progress update due on 5 December 2026. Separately, every large UK business (250-plus employees, or turnover above £44 million with a balance sheet above £38 million) needs to check its position again on 31 December 2026, because that is the qualification date for Phase 4, whether or not it took part in Phase 3.
What Is ESOS, in Plain English?
ESOS stands for the Energy Savings Opportunity Scheme, a mandatory UK energy assessment scheme for large organisations. The Environment Agency runs it in England, with equivalent regulators in Wales, Scotland and Northern Ireland. If your business qualifies, you have to carry out an energy audit every four years, covering the energy used in your buildings, industrial processes, and transport, and then report the findings and what you plan to do about them.
The point of ESOS is not to catch businesses out. It is meant to surface savings that most organisations would not look for on their own. Government research found that businesses tend not to conduct energy audits unless required to, which is exactly why the scheme is mandatory rather than voluntary.
For many businesses, the audit itself becomes far more valuable than the reporting requirement. It often uncovers inefficient equipment, incorrect capacity, unnecessary consumption, and opportunities to reduce future contract costs.
The official ESOS guidance, published jointly by the Department for Energy Security and Net Zero and the Environment Agency, sets out exactly how to assess your energy consumption, choose a compliance route and appoint a Lead Assessor. The summary below covers what most businesses need to know for Phases 3 and 4.
If you want the fuller picture on how an energy audit works in practice, our Business Energy Audits page covers what’s involved and what businesses typically find.
Where Are We in the ESOS Timeline Right Now?
ESOS runs in four-year phases. Phase 3 covered 6 December 2019 to 5 December 2023, with qualification assessed on a single snapshot date: 31st of December 2022.
Phase 4 began immediately afterwards, on 6 December 2023, and runs through to a compliance deadline of 5 December 2027. The two phases overlap on purpose, which is exactly where the confusion tends to start.
Phase 3 Still Has Unfinished Business in 2026
The Phase 3 compliance notification deadline was extended twice, first from 5 December 2023 to 5 June 2024, then with a late submission window to 6 August 2024. That’s not the end of the story. Under the ESOS (Amendment) Regulations 2023, every Phase 3 participant also has to submit a forward-looking action plan (due 5 December 2024, signed off by a board-level director) and then two annual progress updates against it. The first was due on 5 December 2025. The second and final one is due on 5 December 2026.
In other words, if your business took part in Phase 3, you have one more statutory submission to make this year, regardless of anything to do with Phase 4.
A lot of the businesses we speak to think ESOS finished when they submitted their notification back in 2024. It didn’t. Phase 3 still has one more progress update due this December, and Phase 4 qualification is being assessed at the same time. Missing either one because you assumed it was over is an easy way to end up on the wrong side of the Environment Agency.Joe Glendinning, Founder, Renew & Sustain
Phase 4 Qualification Is Closer Than It Looks
Phase 4’s qualification date is 31 December 2026, less than six months from now. Unlike the compliance deadline (5 December 2027), which is when audits and reports are due, the qualification date is simply the day your organisation’s size is measured. If you cross the large undertaking threshold by then, you are in scope for Phase 4, whether or not you were ever part of Phase 3.
Businesses approaching the threshold shouldn’t wait until January 2027 to find out. Checking your position before the qualification date gives you time to plan resources, gather energy data, and schedule an audit without the pressure of approaching deadlines.
Aligning Your ESOS Strategy with the UK Energy Act
Who Needs to Worry About ESOS Phase 4?
Determining your compliance obligations for Phase 4 requires analysing your total corporate footprint. Because thresholds are assessed across entire corporate structures, understanding how group entities, acquisitions, and international parents interact is critical to evaluating your status.
The Large Undertaking Test
An organisation qualifies as a large undertaking if, on the qualification date, it employs 250 or more people in the UK, or has an annual turnover above £44 million, together with a balance sheet total above £38 million. Qualification is assessed across the whole UK corporate group. If a single group entity meets the threshold, the entire UK group is in scope, and UK establishments of overseas companies can be pulled in too if the wider global group meets the criteria.
What If You Weren’t in Scope for Phase 3?
None of this depends on Phase 3 history. A business that has grown through hiring, acquisition or turnover since the 2022 snapshot may qualify for Phase 4 for the first time. Equally, a business that shrank since then may fall out of scope, though it should still tell the Environment Agency it no longer qualifies, rather than simply going quiet.
What Happens During an ESOS Audit?
An ESOS audit follows a set, structured process, starting with real data and ending in a plan you can act on.
It usually opens with site visits, so the assessment reflects how your buildings and operations actually run, not just what is written down on paper. From there, the assessor collects at least 12 months of verifiable energy data across the three areas ESOS covers: buildings, transport and industrial processes, along with any other significant energy use, which together account for at least 95% of your total consumption.
With the data gathered, the focus moves to identifying opportunities: pinpointing where energy is being wasted and where practical, cost-effective changes would make a measurable difference, whether that is heating and lighting in a building, fuel use across a vehicle fleet, or inefficiencies on a production line.
Every ESOS audit must be signed off by an approved Lead Assessor, an independent professional who reviews the methodology and findings before anything is submitted. This sign-off is what makes it a compliant ESOS audit rather than a general energy review.
The process ends with an evidence pack: a record of the data used, the methodology followed, and the recommendations produced, kept on file in case the Environment Agency asks to see it. Done properly, this is also where the audit earns its keep, showing your business in specific terms where money is being spent and where it can be saved.
Our Business Energy Audits team manages this whole process for you, from the initial site visit through to Lead Assessor sign-off and a finished evidence pack, so the requirement becomes a source of savings rather than another item on a compliance checklist.
What Happens if You Get It Wrong
The Environment Agency’s enforcement and sanctions policy sets out civil penalties for ESOS breaches. Reported figures include up to £50,000 for failing to submit a notification of compliance, plus £500 for each day the breach continues, and a similar penalty structure for failing to carry out an energy audit. Failing to maintain an evidence pack or submit an action plan carries penalties of up to £5,000, again with daily fines for continued non-compliance, and false or misleading statements can attract penalties of up to £50,000. Environment Agency enforcement activity against Phase 3 non-compliance has already begun following the final deadline of 6 August 2024.
Beyond the fines, Phase 3 introduced public disclosure of compliance data. The Environment Agency publishes most of what businesses submit, including energy consumption, intensity ratios, action plans and progress reports, on a public register. That means non-compliance or a weak set of results is visible to customers, competitors and anyone conducting due diligence.
Because ESOS audits examine how your organisation uses energy across buildings, transport and industrial processes, many businesses use the exercise to inform procurement decisions, budget planning and future efficiency projects rather than treating it as a standalone compliance exercise.
The financial penalties get the headlines, but the bit that worries most of our clients more is the public register. Once your ESOS status is published, your customers, your competitors, and anyone doing due diligence on your business can see it. That’s a bigger incentive to get this right than the fine itself.Joe Glendinning, Founder, Renew & Sustain
How to Prepare for ESOS Phase 4 Now
With the qualification date less than six months away, the practical priorities are straightforward:
- Check your numbers against 31 December 2026 snapshot: UK headcount, turnover and balance sheet total, across the whole UK corporate group.
- If you took part in Phase 3, get the second progress update ready well before 5 December 2026. It needs board-level sign-off, so build in time for that internally.
- If you are approaching the threshold for the first time, do not wait for a letter from the Environment Agency. Start scoping an ESOS-compliant energy audit now, covering at least 95% of your total energy consumption across buildings, transport and industrial processes.
- Treat the audit as a cost exercise rather than a compliance one. The measures an ESOS audit identifies are meant to pay for the assessment many times over in energy savings.
- Keep an evidence pack as you go, rather than reconstructing one under deadline pressure.
Our Business Energy Audits team can carry out a full ESOS-compliant audit and help with the action plan and progress reporting that go with it, whether this is your first cycle or your third.
Related Reading: How to develop an effective business energy procurement strategy
Why This Matters Even More in Today’s Energy Market
Wholesale gas prices have been unsettled through the summer of 2026. UK and European markets have moved on renewed shipping risk around the Strait of Hormuz, which carries a significant share of global LNG trade, alongside tight Qatari LNG supply and French nuclear outages. European gas storage was around 49% full in early July, well behind the seasonal average of roughly 60%, and analysts expect it to reach only the mid-70s% before winter, leaving prices exposed to further disruption or a cold snap.
Ofgem’s domestic price cap rose 13% for the July to September 2026 period, with gas rates up roughly 24% and electricity up around 5%. There’s no equivalent cap for business energy contracts. Non-domestic customers on a fixed-rate deal are insulated in the short term, but anyone due to renew a contract in the next 12 to 18 months is renewing into a genuinely volatile market.
This is exactly the environment in which an ESOS audit earns its keep twice over. It satisfies a legal obligation and is also one of the more reliable ways to achieve real reductions in consumption before locking in a new energy contract amid today’s uncertain prices. If your organisation operates within heavy manufacturing or critical industrial supply chains, balancing your immediate energy strategy against evolving government schemes is essential for protecting cash flow.
Related Reading: Balancing the EII Support Levy vs BICS Relief
ESOS Phase 3 and Phase 4 FAQs
The questions below cover the points that come up most often when Phase 3 obligations and Phase 4 qualification fall in the same year.
When is the next ESOS deadline for businesses that already took part in Phase 3?
5 December 2026. This is the second and final annual progress update against your Phase 3 action plan, and it needs sign-off from a board-level director before submission through the Manage your ESOS reporting system.
What is the ESOS Phase 4 qualification date?
31 December 2026. Your organisation’s size on this date, measured by UK employee numbers, turnover and balance sheet total, determines whether you are in scope for Phase 4.
What is the ESOS Phase 4 compliance deadline?
5 December 2027. This is when Phase 4 audits, reports, and compliance notifications are due, separate from the earlier qualification date.
Do we need to redo our energy audit for Phase 4 if we already completed one for Phase 3?
Yes. Each phase requires its own ESOS-compliant assessment, based on 12 months of verifiable energy data for that phase, even if your business also took part in Phase 3.
What are the penalties for ESOS non-compliance?
Civil penalties can reach up to £50,000 for failing to notify compliance or failing to carry out an audit, with daily fines for continued breaches, and up to £5,000 for evidence pack or action plan failures. Non-compliance is also published on a public Environment Agency register.
Could our business qualify for ESOS for the first time in Phase 4, even though we were not in scope for Phase 3?
Yes. Qualification is reassessed at every phase. Growth in headcount, turnover or balance sheet total since the last snapshot date can bring a business into scope for the first time.
Ready to Get Ahead of ESOS Phase 4?
Whether Phase 3 is genuinely finished for your business or Phase 4 is about to catch you for the first time, a properly scoped energy audit does both jobs at once: it satisfies your ESOS obligations, and it is usually one of the fastest ways to find real savings before your next contract renewal.
Get in touch with the Renew & Sustain team for a free initial consultation and find out exactly where your business stands before 31 December 2026 qualification date arrives.
Article Sources
- GOV.UK. Energy Savings Opportunity Scheme (ESOS). 16 February 2026
- legislation.gov.uk. Energy Savings Opportunities Scheme (Amendment) Regulations 2023. Accessed 13 July 2026
- GOV.UK/Environment Agency. Environment Agency enforcement and sanctions policy, Annex 2. 10 October 2025
- UK SRS. ESOS Phase 3: Deadlines, Changes and Compliance. Accessed July 13th, 2026
- Ofgem. Changes to the energy price cap between 1 July and 30 September 2026. 27 May 2026.
