Qualification criteria at a glance
What ESOS is
The Energy Savings Opportunity Scheme (ESOS) is a mandatory UK energy assessment regime for large organisations. It operates under the Energy Savings Opportunity Scheme Regulations 20141 (SI 2014/1643), originally enacted to implement Article 8 of the EU Energy Efficiency Directive 2012/27/EU9.
ESOS requires qualifying organisations to undertake an energy audit every four years, identifying opportunities for energy efficiency improvements.
It is administered by the Environment Agency in England6 with equivalent administrators in Scotland, Wales, and Northern Ireland.
Policy lead since February 2023 is the Department for Energy Security and Net Zero (DESNZ)5.
ESOS runs in four-year phases.
Phase 1 ran 2014-2015, Phase 2 ran 2018-2019, Phase 3 ran 2022-2023, and the Phase 4 qualification date is 31 December 20262.
Each phase has its own qualification date, audit period, and compliance deadline.
For what changed this cycle, see ESOS Phase 3 vs Phase 4.
ESOS regulations: the legal instruments behind Phase 4
The ESOS regulations that create the Phase 4 thresholds are the Energy Savings Opportunity Scheme Regulations 20141 (SI 2014/1643), as amended by the ESOS (Amendment) Regulations 20234 (SI 2023/1182).
Two specific provisions do the qualification work: regulation 2(1)2 sets the "large undertaking" thresholds, and regulation 63 sets the group aggregation rules.
The ESOS regulations are enforced in England by the Environment Agency6, with equivalent bodies in Scotland, Wales and Northern Ireland, and administered under Department for Energy Security and Net Zero (DESNZ) policy lead since February 20235.
Knowing which regulation underpins a given requirement — regulation 2(1) for qualification, regulation 6 for aggregation — helps distinguish what the ESOS regulations legally require from what is best-practice guidance.
ESOS legislation: from the EU Energy Efficiency Directive to UK law
The ESOS legislation originates in Article 8 of the EU Energy Efficiency Directive 2012/27/EU9, which required member states to introduce mandatory energy audits for large undertakings.
The UK transposed this obligation into domestic law via the Energy Savings Opportunity Scheme Regulations 20141 (SI 2014/1643).
The original ESOS legislation set the financial thresholds in euros (€50 million turnover, €43 million balance sheet).
The ESOS (Amendment) Regulations 20234 re-denominated these into sterling — £44 million turnover and £38 million balance sheet2 — which are the figures that apply for Phase 4 qualification; the euro figures are historical only.
That 2023 amendment was made under powers in the Energy Act 2023, section 197 and Schedule 1812.
The group provisions within the ESOS legislation draw on the Companies Act 2006 sections 1158-11627 definition of parent-subsidiary relationships, applied to UK-incorporated entities only under regulation 6 of SI 2014/16433.
ESOS Phase 4 qualification criteria assessment — 31 December 2026
The ESOS qualification criteria for Phase 4 are assessed at a single point in time: 31 December 20262.
An organisation's UK group status on this specific date determines whether it is in scope for the entire Phase 4 cycle, regardless of structural changes before or after.
Understanding the ESOS qualification criteria is essential for compliance planning.
The single-date approach has practical consequences2:
- Group structure as at 31 December 2026 — acquisitions completed before this date count toward the group; divestments completed before this date are excluded
- Financial figures — most recent accounts period before 31 December 2026 (for a December year-end, accounts for year ending 31 December 2025) [2]
- Employee headcount — UK group total as at 31 December 2026 [2]
- Structural changes made after 31 December 2026 do not change Phase 4 scope, even if they would have changed qualification status [2]
Phase 4 compliance deadline is 5 December 20275 — notification to the Environment Agency, completion of the energy audit, and submission of the Action Plan.
Phase 4 audit periods cover 12 months of energy use within the 24 months ending on the compliance deadline.
ESOS Phase 4 employee threshold (250+)
The "large undertaking" definition in regulation 2(1) of SI 2014/16432 sets the employee threshold at 250 or more.
The 250+ test counts all employees of UK group entities — parent company and all UK-incorporated subsidiaries.
An organisation qualifies on this test alone, regardless of financial position.
The DESNZ ESOS guidance5 sets out how the headcount is compiled.
The table below summarises what counts — and what is excluded — when measuring the UK group headcount against the 250-employee threshold5.
| Counts toward the 250 employee threshold | Excluded from the count |
|---|---|
| Direct employees of UK group entities — full-time, part-time, fixed-term | Employees of overseas group entities (only UK incorporation counts) |
| Apprentices and trainees on contract | Self-employed contractors and consultants |
| UK group companies and subsidiaries (per group aggregation rules) | Agency workers placed for short periods |
| Workers seconded into the UK group | Dormant relationships — measured on active employment at the qualification date |
For groups straddling the threshold, the qualification date employee count is determinative.
Seasonal businesses must reflect actual headcount at 31 December 2026, not annual average.
ESOS Phase 4 financial thresholds (£44m + £38m)
The "large undertaking" definition in regulation 2(1) of SI 2014/16432 sets two sterling financial thresholds that must be met together.
The original euro figures (€50 million turnover, €43 million balance sheet), inherited from the EU Energy Efficiency Directive 2012/27/EU9, were re-denominated into pounds by the ESOS (Amendment) Regulations 2023 (SI 2023/1182)4 — the sterling figures ARE the legal thresholds, with no exchange-rate conversion involved:
- Annual turnover (revenue) of £44 million or more
- Annual balance sheet total of £38 million or more
Both must be exceeded — meeting only one is insufficient.
An organisation with £100 million turnover but only £30 million balance sheet does NOT qualify on the financial route alone, though it would qualify if it also employs 250+ people via the employee route2.
The financial figures are drawn from the most recent annual accounts period before the qualification date2.
For a UK group with December year-ends, Phase 4 qualification uses accounts for year ending 31 December 2025 (the last full accounting period before 31 December 2026).
Group aggregation applies3 — the figures are UK group consolidated totals, not single-entity figures.
This is examined in detail in the next section.
Group Aggregation Requirements
Parent-subsidiary relationships
Companies where another holds >50% voting rights or dominant influence per Companies Act 2006
Common control entities
Multiple entities under the same ultimate parent must be aggregated
UK scope only
Only UK-incorporated entities count for ESOS aggregation; overseas entities excluded
LLPs and limited partnerships
Subject to the same group definitions as companies
Whole group obligation
If ANY entity qualifies, ENTIRE UK group becomes subject to ESOS
ESOS Phase 4 thresholds: group aggregation rules
Regulation 6 of SI 2014/16433 sets out the group aggregation rules.
The fundamental principle: if ANY single entity in the UK group meets the qualification thresholds at 31 December 2026, the ENTIRE UK group becomes subject to ESOS Phase 4 — including individually sub-threshold entities.
What counts as a group7:
- Parent-subsidiary relationships under the Companies Act 2006 sections 1158-1162 definition — companies where another holds more than 50% of voting rights, or has the right to exercise a dominant influence
- Common control — multiple entities under the same ultimate parent
- UK scope only — only UK-incorporated entities count for ESOS aggregation; overseas group entities are excluded
- LLPs and limited partnerships subject to the same group definitions as companies
Where a UK group's only qualifying entity is a small subsidiary that happens to meet the employee or financial thresholds, the obligation extends across all UK entities — including the parent and other subsidiaries that are individually sub-threshold.
Groups should perform consolidated qualification analysis rather than entity-by-entity.
The Responsible Undertaking
Where a group qualifies for ESOS Phase 4, Regulation 63 requires the group to designate a single entity as the "Responsible Undertaking" with overall responsibility for ESOS compliance across the UK group.
Notifications are made to the Environment Agency6.
Practical mechanics5:
- Designation flexibility — the group selects which entity serves as Responsible Undertaking; typically the UK parent or holding company
- Group-wide coverage — the Responsible Undertaking must ensure energy audits cover the entire UK group, including individually sub-threshold subsidiaries
- Single compliance notification — one notification submitted to the Environment Agency on behalf of the group
- Legal responsibility — the designated entity bears full legal responsibility for compliance; penalties for non-compliance fall on the Responsible Undertaking
- Change of designation — possible mid-phase but requires notification to the Environment Agency
Acquisitions, divestments, and reorganisations
Structural changes around the qualification date can affect Phase 4 scope, governed by the group provisions in Regulation 6 of SI 2014/16433:
Acquisitions
Companies acquired before 31 December 2026 count toward qualification thresholds3.
The acquired entity becomes part of the UK group for ESOS purposes; its employees, turnover, and balance sheet aggregate with the existing group.
The acquired entity's energy consumption must be included in the Phase 4 audit scope.
Historical energy data for the acquired entity may be limited if it was not previously in ESOS scope.
Divestments
Companies sold before 31 December 2026 do not count toward qualification3.
They are excluded from employee headcount, turnover, and balance sheet.
If the divested entity continues to be a qualifying undertaking in its own right, it has its own Phase 4 obligations under its new ownership.
Reorganisations
Internal restructuring may change qualification status without changing the underlying business3.
Splitting a single qualifying entity into smaller entities may reduce individual entity headcount but does not change UK group aggregation.
Moving entities between UK and overseas group locations affects the UK-only scope of ESOS.
Legal entity structure as at 31 December 2026 is determinative.
Groups planning structural changes around the qualification date should take specific legal advice.
The single-date qualification test means that planning windows close hard on 31 December 2026.
Out-of-scope cases
Certain organisations fall outside the ESOS Phase 4 thresholds entirely and are out of scope under the Energy Savings Opportunity Scheme Regulations 20141.
The categories below sit outside the qualification tests:
Organisations outside the ESOS Phase 4 thresholds
Public sector bodies
Central government, local authorities, NHS trusts and public corporations. Separate frameworks apply, e.g. the Greening Government Commitments.
Sub-threshold UK groups
Groups not meeting any of the qualification tests at 31 December 2026 — below the employee and both financial thresholds.
Sole traders & partnerships
General partnerships and sole traders have limited legal structure for ESOS obligations, with specific exceptions in the regulations.
Trusts & unincorporated associations
Generally out of scope, though specific cases require individual legal analysis.
Dormant companies
No significant business activity, and hence no meaningful energy consumption to assess.
Overseas-incorporated entities
Only UK-incorporated entities count for ESOS group aggregation; overseas entities are excluded.
Public bodies instead report under frameworks such as the Greening Government Commitments5.
Organisations near the threshold or with unusual structures (mixed public/private group, charity with trading subsidiaries, holding company without operations) should take legal advice on their specific position.
ESOS Phase 4 threshold examples: who qualifies
Applying the ESOS Phase 4 thresholds to real group structures is where qualification decisions are usually won or lost.
The worked examples below show how the employee test, the paired financial tests, and group aggregation combine at the 31 December 2026 qualification date2.
| Organisation profile | Against the thresholds | Phase 4 outcome |
|---|---|---|
| UK group, 320 employees, £30m turnover, £20m balance sheet | Employee test met (250+); financial tests not met | Qualifies — the employee test qualifies on its own |
| UK company, 90 employees, £60m turnover, £45m balance sheet | Both financial tests met (£44m+ AND £38m+); employee test not met | Qualifies — both financial thresholds are exceeded together |
| UK company, 90 employees, £60m turnover, £20m balance sheet | Only one financial test met; employee test not met | Does not qualify — turnover alone is insufficient on the financial route |
| UK group with a 400-employee subsidiary under a sub-threshold parent | One entity meets the employee test; group aggregation applies | Entire UK group qualifies, including the sub-threshold parent [3] |
| UK parent, 500 UK employees, plus a 2,000-employee overseas subsidiary | Only UK-incorporated headcount counts | Qualifies on UK headcount; overseas employees are excluded |
The recurring theme: the employee test (250+) is a standalone route, the two financial tests only work as a pair, and group aggregation3 can pull an otherwise sub-threshold parent into scope through a single qualifying subsidiary.
Where a group sits close to any threshold, run the assessment on the projected 31 December 2026 structure rather than today's.
Common ESOS Phase 4 qualification mistakes
Most ESOS Phase 4 qualification errors trace back to a handful of recurring misreadings of the thresholds and the group rules2.
The list below covers the ones Lead Assessors and the Environment Agency see most often.
- Treating the financial tests as either/or — turnover £44m+ and balance sheet £38m+ must both be met; meeting one is not enough on the financial route [2]
- Assessing single entities instead of the UK group — if any one UK entity qualifies, the whole UK group is in scope, so entity-by-entity checks understate the obligation [3]
- Counting overseas headcount or turnover — only UK-incorporated entities count toward ESOS aggregation; overseas group members are excluded [3]
- Using the wrong accounts period — financial figures come from the most recent accounts before 31 December 2026 (year ending 31 December 2025 for a December year-end), not the current in-progress year [2]
- Assuming a post-date reorganisation changes scope — structural changes after 31 December 2026 do not alter Phase 4 qualification, even if they would have changed the result [2]
- Forgetting the DEC and GDA routes are gone — Phase 4 compliance is via an ESOS energy audit or ISO 50001 only; participants who relied on Display Energy Certificates or Green Deal Assessments in earlier phases must switch [5]
Each of these is avoidable with a consolidated, UK-group-level qualification assessment run against the projected 31 December 2026 position.
For the full step-by-step route from qualification to notification, see our ESOS compliance guide.
Seven steps from qualification to compliance
Qualification check
- Assess UK group against three tests
- Aggregate group entities
- Confirm qualification status
Lead assessor engagement
- Identify ESOS Lead Assessor
- Sign engagement agreement
- Define audit scope
Data collection
- Gather 12 months energy data
- Compile site information
- Document energy uses
Energy audit
- 90%+ energy coverage audit
- Site visits as required
- Identify efficiency opportunities
Action plan
- Prioritize opportunities
- Create implementation plan
- Board sign-off
Compliance notification
- Complete notification template
- Director sign-off
- Submit to Environment Agency
Record keeping
- Maintain audit evidence
- Track implementation progress
- Prepare for Phase 5
Compliance routes after meeting ESOS Phase 4 qualification criteria
Meeting the ESOS qualification criteria determines whether ESOS applies.
Compliance — the actual energy assessment and reporting — follows defined routes set out in SI 2014/16431 and updated by SI 2023/11824.
The ISO 50001 certified energy management system is one alternative compliance route.
- ESOS energy audit — undertaken by a registered Lead Assessor covering 90%+ of total energy consumption. The default compliance route
- ISO 50001 [8] certified energy management system covering 100% of UK energy consumption — substitutes for the energy audit requirement entirely
- Hybrid combinations — ISO 50001 covering some sites/uses, ESOS audit covering the remainder
Display Energy Certificates (DECs) and Green Deal Assessments (GDAs) were removed as ESOS compliance routes for Phase 45.
Participants relying on these routes in earlier phases must move to an ESOS energy audit or ISO 50001 for Phase 4.
The ESOS (Amendment) Regulations 2023 (SI 2023/1182)4 introduced significant Phase 3 enhancements that carry into Phase 4: energy intensity ratios, Action Plan submission requirement, mid-phase Progress Updates, and enhanced site-level reporting.
Phase 4 entrants should plan for full implementation of these enhanced requirements.
The audit period covers 12 months of energy use within the 24 months ending on the compliance deadline (5 December 2027)5.
Many organisations use the most recent complete financial year as the audit reference period.
ESOS Phase 4 requirements: energy audits, action plans and changes from Phase 3
Once an organisation qualifies, the ESOS Phase 4 requirements are to measure total energy consumption, audit at least 95% of it, produce a board-approved action plan, and notify the Environment Agency before 5 December 20275.
Phase 4 carries forward the enhancements first introduced mid-cycle by the ESOS (Amendment) Regulations 20234.
Energy audit requirements
The ESOS energy audit must cover 95% of the organisation's total UK energy consumption across all energy types — electricity, gas, transport fuels, and other sources5.
The 5% de minimis allowance lets minor uses be excluded where auditing them would be disproportionate.
Audits are conducted by a registered Lead Assessor using at least 12 months of consumption data, and must identify energy-efficiency opportunities with cost-benefit analysis and estimated payback5.
Mandatory action plans
The headline Phase 4 change is the mandatory action plan under Part 6A of SI 2023/11824.
Every qualifying organisation must set out the energy-efficiency measures it intends to take, obtain board-level sign-off, and submit the plan alongside its notification.
Participants must then report annual progress against the commitments in that plan4 — deadlines, sign-off, and publication are covered in our ESOS action plan guide.
What changed from Phase 3
- Mandatory, board-approved action plans with annual progress updates (Part 6A, SI 2023/1182)4
- Display Energy Certificates (DECs) and Green Deal Assessments (GDAs) removed as compliance routes — only the ESOS audit or ISO 50001 remain [5]
- Enhanced site-level reporting and energy-intensity ratios carried in from the 2023 amendment [4]
- Mandatory net-zero requirements deferred to Phase 5 (2027–2031) rather than introduced for Phase 4 [5]
ESOS requirements checklist: what qualifying organisations must do
Once an organisation meets the ESOS Phase 4 thresholds, the ESOS requirements are the same regardless of which qualification route applied.
The checklist below draws together the obligations covered in detail earlier in this guide.
- Notify the Environment Agency of qualification and compliance by 5 December 2027 [5]
- Complete an energy audit covering at least 95% of total UK energy consumption, or hold an ISO 50001 certified energy management system covering 100% [8]
- Produce a board-approved action plan and submit it alongside the compliance notification, under Part 6A inserted by SI 2023/1182 [4]
- Report annual progress against action plan commitments, with an explanation required where commitments have not been met [4]
- Designate a single Responsible Undertaking with group-wide compliance responsibility [3]
- Maintain compliance records — failure to do so risks a civil penalty of up to £5,000 [6]
These ESOS requirements apply across the whole UK group once any single entity qualifies3 — see group aggregation above.
For the full step-by-step compliance pathway, see our ESOS compliance guide.
Penalties for non-compliance
The Environment Agency enforces ESOS in England6 with equivalent enforcement bodies in devolved nations.
Penalties for missing the ESOS Phase 4 requirements can be substantial, as set out in the EA Enforcement and Sanctions Policy:
- Failure to undertake an energy audit — civil penalty up to £50,000 plus £500 per day continuing [6]
- Failure to notify compliance — civil penalty up to £5,000 plus £500 per day continuing [6]
- Failure to maintain records — civil penalty up to £5,000 [6]
- Publication — penalty notice details published by the Environment Agency, including organisation name [6]
The Environment Agency6 publishes annual ESOS compliance statistics.
Phase 3 enforcement actions established that the EA exercises its penalty powers, including against well-known organisations.
Audit committees should treat ESOS compliance as a reputational risk alongside the financial penalty exposure.
For the full penalty framework — audit failure, notification failure, and daily penalties — see our ESOS penalties and enforcement guide.
ESOS deadlines: qualification, notification and action plan dates
The ESOS Phase 4 deadlines fall into three groups: the qualification assessment date, the compliance and notification deadline, and the ongoing action plan reporting cadence.
| Deadline | Date | What's due |
|---|---|---|
| Phase 4 qualification date | 31 Dec 2026 | UK group status assessed against the three tests [2] |
| Phase 4 compliance deadline | 5 Dec 2027 | Notification, energy audit completion and board-approved action plan submitted to the Environment Agency [5] |
| Action plan progress updates | Annually, within the phase | Progress against action plan commitments reported, with an explanation required where commitments are missed [4] |
| Phase 5 | 2027–2031 | Next ESOS cycle; mandatory net-zero requirements postponed to this phase [5] |
Missing any of these ESOS deadlines carries a civil penalty risk — up to £50,000 plus £500 per day continuing for a missed energy audit, and up to £5,000 plus £500 per day continuing for a missed notification6.
See penalties above for the full enforcement framework.
ESOS vs UK SRS: Key Differences
Legal basis
ESOS: SI 2014/1643 under DESNZ | UK SRS: FCA listing rules and Companies Act 2006
Scope determinant
ESOS: Size thresholds (250+ employees or financial tests) | UK SRS: Listing status (UKLR categories)
Content focus
ESOS: Operational energy audit with efficiency opportunities | UK SRS: Investor-facing climate disclosures
Primary audience
ESOS: Environment Agency and management | UK SRS: Investors and lenders
Data overlap
Both use Scope 1 and 2 emissions data, but analytical depth and presentation differ
How ESOS sits alongside UK SRS
The Energy Savings Opportunity Scheme Regulations 20141 and the UK Sustainability Reporting Standards10 are separate regulatory regimes that may apply concurrently to the same organisation.
The two are distinct in legal basis, scope, content, and audience — as summarised below.
| Dimension | ESOS | UK SRS |
|---|---|---|
| Legal basis | Energy Savings Opportunity Scheme Regulations 2014 (SI 2014/1643) under DESNZ policy lead | Published by DBT on 25 February 2026 under FCA listing rules and the Companies Act 2006 framework |
| Scope determinant | UK group size — 250+ employees, OR £44m turnover AND £38m balance sheet | Listing status (FCA CP26/5 for UKLR 6, 14, 15, 16, 22); private extension awaiting MCR consultation |
| Content | Operational energy audit identifying efficiency opportunities, with quantified savings potential | Investor-facing disclosures across four pillars, with Scope 1, 2 and 3 emissions |
| Primary audience | Environment Agency notification; senior management responsible for energy action | Investors, lenders and other creditors; audit committee oversight |
Many large UK organisations will be subject to both — a UK-listed company with 250+ UK employees may need both ESOS Phase 4 compliance and UK SRS S2 reporting.
The data infrastructure overlap (Scope 1 and 2 emissions, energy use by site) supports both regimes; the analytical depth and audience differ substantially.
SECR (Streamlined Energy and Carbon Reporting, SI 2018/1155)11 is a third regime that also operates alongside both ESOS and UK SRS.
For integrated compliance across all three regimes, see our integrated ESOS, SECR and UK SRS compliance guide.
Frequently asked questions
When is the ESOS Phase 4 qualification date?
ESOS Phase 4 qualification is assessed at a single point in time: 31 December 2026 [2]. An organisation's UK group status on this specific date determines whether it is in scope for the entire Phase 4 cycle.
What are the three ESOS qualification thresholds?
Per the "large undertaking" definition in regulation 2(1) of SI 2014/1643 as amended [2]: (1) employee test — 250+ employees in UK group; or (2) and (3) financial tests — annual turnover of £44m+ AND balance sheet total of £38m+ (both must be met together, in sterling per SI 2023/1182). Meeting only one financial test is insufficient.
Does meeting just the turnover test qualify me for ESOS?
No. The two financial tests work together — both turnover £44m+ AND balance sheet £38m+ must be met. Meeting only one financial test is not sufficient on the financial route. The employee test (250+) qualifies on its own [2].
How do group aggregation rules work?
Per Regulation 6 of SI 2014/1643 [3]: if ANY single entity in the UK group meets the qualification thresholds, the ENTIRE UK group becomes subject to ESOS — including individually sub-threshold entities. Group definition uses Companies Act 2006 sections 1158-1162 [7]. Only UK-incorporated entities count; overseas entities are excluded.
What about acquisitions or divestments before the qualification date?
Companies acquired before 31 December 2026 count toward qualification thresholds and must be included in the Phase 4 audit scope [3]. Companies sold before 31 December 2026 do not count toward qualification and are excluded. Internal reorganisations may change qualification without changing the underlying business — groups planning structural changes around the qualification date should take legal advice.
When is the Phase 4 compliance deadline?
The Phase 4 compliance deadline is 5 December 2027 [5]. By that date, qualifying organisations must notify the Environment Agency, complete the energy audit, and submit the Action Plan. Audit periods cover 12 months of energy use within the 24 months ending on the compliance deadline.
What are the penalties for non-compliance?
Per Environment Agency guidance [6]: failure to undertake an energy audit attracts a civil penalty of up to £50,000 plus £500 per day continuing. Failure to notify compliance attracts up to £5,000 plus £500 per day continuing. Penalty notice details are published by the Environment Agency, including the organisation name [6].
Does ESOS replace or align with UK SRS?
Neither — ESOS and UK SRS are separate regulatory regimes. ESOS [1] is an energy assessment regime under SI 2014/1643 with operational focus; UK SRS [10] is an investor-facing sustainability disclosure regime under FCA CP26/5 with investor focus. An organisation may be subject to one, both, or neither. Many large UK organisations will be subject to both, with data infrastructure overlap on Scope 1 and 2 emissions.
