ESOS thresholds — who qualifies for Phase 4

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 It operates under the Energy Savings Opportunity Scheme Regulations 20141 (SI 2014/1643), originally enacted to implement Article 8 of the EU Energy Efficiency Directive 2012/27/EU9.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 Phase 4 qualification date is 31 December 20262. Each phase has its own qualification date, audit period, and compliance deadline.

Phase 4 qualification date — 31 December 2026

ESOS Phase 4 qualification is 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.

The single-date approach has practical consequences:

• Group structure as at 31 December 2026 — acquisitions completed before this date count toward the group; divestments completed before this date are excluded [3]
• 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 6 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.

The employee test (250+)

Regulation 5 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.

What counts toward the employee total5:

• Direct employees of UK group entities — full-time, part-time, fixed-term
• Apprentices and trainees on contract
• Contractors working exclusively for the UK group (working pattern test, not contract type)
• Workers seconded into the UK group

What does NOT count5:

• Employees of overseas group entities (only UK incorporation counted)
• Self-employed contractors working for multiple clients
• Agency workers placed for short periods
• Pensioners and individuals on parental leave (these are counted, but the calculation is 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.

The financial tests (£44m turnover AND £38m balance sheet)

Regulation 5 of SI 2014/16432 sets two financial thresholds that must be met together:

• 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 route.

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 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 [7] 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.

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 scope3:

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 are out of ESOS scope under SI 2014/16431:

• Public sector bodies — central government, local authorities, NHS trusts, public corporations. Separate energy efficiency frameworks apply (e.g. Greening Government Commitments [5])
• Sub-threshold UK groups — groups not meeting any of the qualification tests at 31 December 2026
• Sole traders and general partnerships — limited legal structure for ESOS obligations (with specific exceptions in the regulations [1])
• Trusts, unincorporated associations — generally out of scope, though specific cases require analysis
• Dormant companies — no significant business activity, hence no meaningful energy consumption to assess
• Overseas-incorporated entities — only UK-incorporated entities count for ESOS group aggregation [3]

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.

Compliance routes after qualification

Qualification 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
• Display Energy Certificates (DECs) — for qualifying public buildings
• Green Deal Assessments — for certain commercial premises (route largely deprecated post-Green Deal scheme closure)
• Hybrid combinations — ISO 50001 covering some sites/uses, ESOS audit covering the remainder

SI 2023/11824 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 (6 December 2027)5. Many organisations use the most recent complete financial year as the audit reference period.

Penalties for non-compliance

The Environment Agency enforces ESOS in England6 with equivalent enforcement bodies in devolved nations. Penalties for non-compliance can be substantial:

• 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.

How ESOS sits alongside UK SRS

ESOS1 and UK SRS10 are separate regulatory regimes that may apply concurrently to the same organisation. The two are distinct in legal basis, scope, content, and audience.

Legal basis110:

• ESOS — Energy Savings Opportunity Scheme Regulations 2014 (SI 2014/1643) under DESNZ policy lead
• UK SRS — published by DBT on 25 February 2026 under FCA listing rules and Companies Act 2006 framework

Scope determinants210:

• ESOS — UK group size (250+ employees, OR £44m turnover AND £38m balance sheet)
• UK SRS — listing status (FCA CP26/5 for UKLR 6, 14, 15, 16, 22 listed companies); private extension awaiting MCR consultation

Content510:

• ESOS — operational energy audit, identifying opportunities for energy efficiency improvements, with quantified savings potential
• UK SRS — investor-facing sustainability disclosures, four-pillar framework covering governance, strategy, risk management, metrics and targets, with Scope 1, 2, and 3 emissions

Audience510:

• ESOS — Environment Agency (compliance notification); senior management responsible for energy efficiency action
• UK SRS — investors, lenders, other creditors (primary users); 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.

SECR11 (Streamlined Energy and Carbon Reporting under SI 2018/1155) is a third regime that also operates alongside both ESOS and UK SRS — covered in subsequent moonshots in this regulatory-overlap cluster.

Frequently asked questions