ESOS
What is ESOS?
If your business is large enough, energy efficiency is not just good practice, it is the law. ESOS, the Energy Savings Opportunity Scheme, makes large UK organisations audit their total energy use every four years and report the savings they could make. It does not force you to act on what the audit finds, but it does force you to look. For a qualifying business the deadlines are real, the penalties are steep, and the next compliance date, 5 December 2027, is closer than it looks. Here is what ESOS is and whether it applies to you.
On this page
ESOS is a compliance scheme, not a tax or a levy. It applies only to large undertakings, and it is administered by the Environment Agency. If your business qualifies, missing a deadline is expensive; if it does not, ESOS is simply useful background.
What ESOS is
ESOS is the UK’s mandatory Energy Savings Opportunity Scheme. It requires large organisations to carry out a detailed assessment of their energy use, covering buildings, transport and industrial processes, once every four years, and to identify cost-effective ways to cut consumption. The scheme is administered by the Environment Agency, which acts as the compliance body for the whole of the UK.
The core idea is simple: large energy users are made to measure what they use and find where they could save. What they do about it is largely up to them, but the act of looking is compulsory.
Who qualifies
ESOS applies to large undertakings. A UK business qualifies if, on the qualification date, it meets either of these tests:
- It employs 250 or more people, or
- It has an annual turnover above around £44m and a balance sheet total above around £38m.
Corporate groups are assessed together, so smaller companies that are part of a large group can be pulled in. Most small and medium businesses fall outside ESOS entirely. If you are not sure whether your group qualifies, the employee and financial thresholds on the qualification date are the place to start.
What an ESOS assessment involves
An ESOS assessment has three broad parts:
- Measure total energy consumption across the organisation, including buildings, industrial processes and transport, over a 12-month period.
- Audit the areas of significant consumption to identify cost-effective energy savings opportunities.
- Report and notify the Environment Agency that the assessment is complete, signed off at board level and reviewed by a lead assessor.
The audit has to cover at least 95% of your total energy consumption, so you cannot simply cherry-pick the easy sites.
The routes to compliance
There is more than one way to satisfy ESOS. Most organisations use ESOS energy audits, but the audit requirement can also be met through other recognised evidence:
| Route | What it is |
|---|---|
| ESOS energy audits | The standard route: audits of your significant energy use carried out for the scheme |
| ISO 50001 | A certified energy management system covering your energy use can satisfy the requirement |
| Display Energy Certificates | DECs for qualifying buildings can count towards the buildings element |
| Green Deal Assessments | Valid assessments can contribute to the evidence |
Many large organisations use a mix, covering buildings one way and transport or processes another, as long as the whole picture meets the 95% threshold.
Compliance phases and deadlines
ESOS runs in four-year compliance phases, each with its own qualification date and deadline. The scheme is currently working towards Phase 4:
| Item | Phase 4 |
|---|---|
| Qualification date | 31 December 2026 |
| Compliance deadline | 5 December 2027 |
| Compliance period | 6 December 2023 to 5 December 2027 |
Miss the deadline and the penalties are significant: failure to carry out an ESOS assessment can attract a penalty of up to £50,000 plus £500 for each day of continued non-compliance. That is why qualifying businesses tend to start well ahead of the date.
The lead assessor
Every ESOS assessment must be reviewed and signed off by an approved lead assessor, an individual on an approved register who checks that the audit meets the scheme’s standards. The lead assessor can be internal if suitably qualified, but most organisations use an external consultant. A board-level director must also sign off the assessment, which keeps energy on the leadership agenda rather than buried in facilities.
Action plans and reporting
Later phases of ESOS added more than a one-off audit. Qualifying organisations are now expected to produce an action plan setting out the energy-saving measures they intend to take, and to report progress against it. This shifts ESOS from a box-ticking audit towards something closer to an ongoing efficiency commitment, even though acting on any given measure remains voluntary.
The practical value is that a good ESOS audit hands you a costed list of savings opportunities. Treated seriously, it can pay for itself several times over through lower electricity and gas bills.
A worked example
Suppose a qualifying business spends £400,000 a year on energy, and its ESOS audit identifies cost-effective measures, better controls, lighting, and process tweaks, worth a 10% reduction:
£400,000 × 10% = £40,000 a year saved if the measures are implemented.
Example only. Actual savings depend entirely on your sites and which measures you act on, so treat this as illustrative rather than a promise.
The audit itself is a cost, but the point of the example is that acting on even a fraction of what it finds can outweigh both the audit fee and the risk of a penalty. ESOS is cheapest to treat as an opportunity rather than a chore.
ESOS vs SECR
ESOS is often confused with SECR, Streamlined Energy and Carbon Reporting, but they are different schemes:
| Scheme | What it does |
|---|---|
| ESOS | A four-yearly energy audit for large undertakings, identifying savings opportunities |
| SECR | An annual disclosure of energy use and carbon emissions in your company accounts |
Many large businesses fall under both. ESOS is the deep audit every four years; SECR is the lighter annual reporting that appears in your financial statements.
What it means for your business
If your organisation qualifies, ESOS is a legal obligation with hard deadlines, so the key is to know your qualification status early and appoint a lead assessor in good time. If it does not qualify, ESOS still points to a useful discipline: measuring your energy use and hunting for savings is worthwhile whatever your size. Even without a statutory audit, reviewing your consumption data and your contract is where most businesses find the quickest wins. That is the same logic that makes a regular bill validation and market review worthwhile for a business of any size.
Frequently asked questions
What is ESOS?
ESOS is the UK’s mandatory Energy Savings Opportunity Scheme. It requires large organisations to audit their total energy use across buildings, transport and processes every four years and identify cost-effective savings. It is administered by the Environment Agency.
Does ESOS apply to my business?
Only if you are a large undertaking. You qualify if you employ 250 or more people, or have annual turnover above around £44m and a balance sheet above around £38m. Corporate groups are assessed together. Most small and medium businesses fall outside ESOS.
When is the ESOS Phase 4 deadline?
The Phase 4 compliance deadline is 5 December 2027, with a qualification date of 31 December 2026. The compliance period runs from 6 December 2023 to 5 December 2027.
What does an ESOS assessment involve?
Measuring total energy consumption over 12 months, auditing the areas of significant use to find cost-effective savings, and notifying the Environment Agency once the assessment is signed off by a lead assessor and a board-level director. The audit must cover at least 95% of your energy use.
What are the routes to ESOS compliance?
Most organisations use ESOS energy audits, but the requirement can also be met through a certified ISO 50001 energy management system, Display Energy Certificates for qualifying buildings, or Green Deal Assessments. Many use a mix that together covers 95% of energy use.
Do I have to act on what an ESOS audit finds?
Not for the audit itself, acting on the identified measures is largely voluntary. However, later phases require an action plan and progress reporting, which nudges organisations towards implementing savings rather than just cataloguing them.
What is an ESOS lead assessor?
An approved individual on a recognised register who reviews and signs off your ESOS assessment to confirm it meets the scheme’s standards. They can be internal if qualified, but most organisations appoint an external consultant.
What are the penalties for missing ESOS?
They are significant. Failure to carry out an ESOS assessment can attract a penalty of up to £50,000 plus £500 for each day of continued non-compliance. Failure to notify can attract up to £5,000 plus £500 per day, alongside publication of the breach.
How often does ESOS happen?
Every four years. ESOS runs in four-year compliance phases, each with its own qualification date and compliance deadline. Qualifying organisations must complete a fresh assessment each phase.
Can ESOS actually save money?
Yes, that is its practical value. A good audit produces a costed list of savings. As an illustration only, a business spending £400,000 a year that acts on measures worth a 10% cut would save around £40,000 a year. Actual savings depend on your sites and choices.
What is the difference between ESOS and SECR?
ESOS is a four-yearly energy audit for large undertakings that identifies savings opportunities. SECR, Streamlined Energy and Carbon Reporting, is an annual disclosure of energy use and carbon emissions within your company accounts. Many large businesses fall under both.
Who administers ESOS?
The Environment Agency is the compliance body for ESOS across the UK, handling notifications, guidance and enforcement. Other environmental regulators support delivery in the devolved nations.
Does ESOS cover transport and vehicles?
Yes. An ESOS assessment covers total energy consumption, which includes transport and fleet energy alongside buildings and industrial processes. Transport is often a significant and overlooked share of a large organisation’s energy use.
Does ISO 50001 exempt me from ESOS?
If a certified ISO 50001 energy management system covers your entire energy use, it can satisfy the ESOS audit requirement, though you still need to notify the Environment Agency. Where it covers only part, you make up the rest through other routes.
Can I use ESOS to cut my energy bills?
Yes. A good ESOS audit produces a costed list of energy-saving opportunities. Acting on them, alongside reviewing your supply contract, is how the audit can pay for itself through lower electricity and gas bills.