Most organisations think of ESOS as just an audit, a signature, or a notification, often filed and forgotten for four years.
The ones getting value from it treat the audit as the input to something else. Phase 4 asks you to identify cost effective energy savings opportunities, produce a board approved action plan, and report the savings you have actually achieved since last time. That is the skeleton of a decarbonisation programme, paid for out of a compliance budget you have to spend anyway.
Same money. Very different outcome. Here is what the dates and the costs actually look like, and how to make the second version happen.
The Dates
ESOS Phase 4 runs from 6 December 2023 to 5 December 2027.
- 31 December 2026: qualification date. Your size is assessed on this day.
- 5 December 2027: notification deadline. Your compliance notification must be with the Environment Agency via the MESOS portal.
- December 2026: Phase 3 progress update. If you were in Phase 3, your second progress update falls due, and it is easy to miss while attention shifts to Phase 4.
You qualify as a large undertaking if, on the qualification date, you have 250 or more UK employees, or turnover above £44 million and a balance sheet total above £38 million. The employee test stands alone; the financial test needs both figures.
Two group points. If any UK group member qualifies, the whole UK group is in scope. And qualification is reassessed every phase, so organisations that were out last time can be caught now, while those that no longer qualify should file a Do Not Qualify notification rather than assuming silence is enough.
Your reference period is twelve consecutive months including 31 December 2026, ending before the deadline. The data you need is being generated right now.
What You Are Paying For
Phase 4 requires you to measure total energy consumption across buildings, transport and industrial processes, audit at least 95% of it, calculate energy intensity ratios, report estimated savings since your last compliance period, produce a board approved action plan, have it signed off by an approved lead assessor, and notify. Then publish the action plan and report progress against it.
That last part is why treating ESOS as a one off filing no longer works. The obligation continues past the deadline.
What Drives Carbon Audit Costs
Quotes for the same scope vary widely. The variation comes from a short list:
- Site visits, which follow from sampling design. You do not have to audit every site. Similar sites can be clustered and representative ones audited on behalf of the group. This is the single largest cost lever, and a provider proposing to visit everything is either not thinking or pricing by the day.
- Estate diversity. Forty near identical units sample well. Forty different building types and processes do not.
- Data quality at the start. Complete half hourly and invoice data is cheap to work with. Gaps, estimates and missing landlord data are expensive, and get more expensive the later they surface.
- Transport. Fleet, HGV, grey fleet and mileage claims all count, and are usually the least well recorded.
- Entity count. More entities means more consolidation and more sign off.
- ISO 50001 coverage, which can remove sites from audit scope entirely.
- Timing. Around nine thousand organisations share one deadline and lead assessor capacity is finite. Late movers pay more and choose from whoever is left.
The pattern across previous phases is consistent: the work does not shrink as the deadline approaches, but the price rises and the choice narrows.
How Carbon Reduction Planning Supports ESOS Compliance
This is where the same budget produces a different result, and it works in both directions.
Phase 4 asks what you actually achieved. You must report estimated energy savings since your previous compliance period. If nothing was implemented after Phase 3, that section is thin, and it is visible to the Environment Agency and to your board. Organisations that acted on their last action plan have something to report. Those that filed and forgot do not.
The action plan is a board document. It requires director level sign off, which means once a year you have senior attention on energy and carbon whether you sought it or not. Drafted as a compliance artefact, it gets approved and shelved. Drafted as a decarbonisation plan with costs, paybacks and owners, it becomes the funding case you have been trying to make.
The audit output feeds everything else. ESOS identifies cost effective energy savings opportunities with quantified paybacks. That same analysis supports your SECR energy efficiency narrative, feeds a Carbon Reduction Plan where you are bidding under PPN 006, and provides implementation evidence for science-based targets SBTi work. The Corporate Net-Zero Standard Version 2.0, published in June 2026, puts more weight on implementation and progress than on target setting alone, and an ESOS audit is one of the few places where a UK organisation gets a costed list of measures as a statutory output.
One dataset, four uses. The energy data gathered for ESOS is the same data behind your SECR disclosure, your Carbon Reduction Plan and your Scope 1 and 2 inventory. Collecting it once and reusing it is the largest efficiency available in this area, and it is entirely a function of how you set the project up at the start.
The practical question to ask a provider is simple: at the end of this, what do I have besides a notification?
Choosing Between ESOS Providers UK Wide
Six questions that separate providers quickly:
- Are your lead assessors in house or subcontracted, and will the same person cover my estate?
- What sampling strategy would you propose, and how many site visits does it imply?
- Is this a fixed fee for the full scope, or a base fee plus day rates?
- Does it include the action plan, the notification and the subsequent progress updates?
- Does the energy data collected feed my SECR reporting and carbon reduction planning, or stop at ESOS?
- Do I get a named contact who knows my sites?
A Sensible Sequence
| Period | Focus |
|---|---|
| Now to late 2026 | Map sites, meters and leases. Collect reference period data as it is generated. Open landlord conversations |
| Late 2026 | Run the qualification test. File a DNQ if applicable. Agree sampling and appoint while capacity is good |
| 2027 | Audits, intensity ratios, action plan drafting, board approval |
| Well before 5 Dec 2027 | Notify |
| After | Publish the action plan, implement, report progress |
The organisations that find Phase 4 straightforward treat 2026 as the data year and 2027 as the audit year. The ones that struggle attempt both in nine months.
Common Mistakes
- Assuming Phase 3 scope still applies. Growth and acquisitions change the answer.
- Leaving landlord data late. It is the longest lead time item in the project.
- Accepting a site visit schedule without questioning the sampling. That is where the money is.
- Treating notification as the finish line. The action plan and progress updates follow.
- Filing the action plan and doing nothing. Phase 4 asks what you achieved, and empty is an answer.
How Enistic Approaches ESOS Compliance And Carbon Reduction
We have guided organisations through every phase of ESOS since the scheme began, alongside more than twenty years of UK energy and carbon work. Our ESOS Lead Assessors, carbon consultants and auditors are all employed in house, and our founder has personally acted as responsible Lead Assessor on hundreds of ESOS audits.
The difference in practice is what you are left holding. Our platform is built and maintained in house, so the energy data gathered for Phase 4 stays live and feeds your SECR disclosure, your Carbon Reduction Plan and your wider decarbonisation work, rather than being collected again next year by someone else.
- 5,000+ compliant reports delivered.
- 100% compliance record, with no failures.
- 80% reduction in data collection burden through platform automation.
- 11.7% audit rate, against an industry average of 33%.
- 98% client renewal rate.
- 24 hours to report delivery once your data is complete.
One consultant is named to your account and stays across the phase, learning which of your sites are complicated. One simple monthly payment, unlimited expert support, no day rates once the audits begin.
The deadline will not move and assessor capacity will not expand to meet it. The organisations with the most choice, and the best price, are the ones deciding now.
Book a demo and we will confirm whether you qualify on 31 December 2026, show you how few site visits your estate actually needs, and set out what the audit could give you beyond the notification.