UK ESOS Compliance Guide

What is ESOS?

The Energy Savings Opportunity Scheme (ESOS) is a mandatory energy assessment scheme for UK organisations that meet the qualification criteria, established by The Energy Savings Opportunity Scheme Regulations 2014.

ESOS applies to large enterprises and requires them to undertake comprehensive assessments of energy used by their buildings, industrial processes and transport.

ESOS Qualification Criteria

Your organisation is a "large undertaking" for ESOS if it meets either of the following tests per the GOV.UK ESOS guidance:

• Employee test: 250 or more employees
• Financial test: Annual turnover exceeding £44 million and balance sheet total exceeding £38 million

Note the structure: there is an OR between the two limbs but an AND inside the financial limb, so exceeding the turnover figure alone does not qualify you.

Group aggregation also applies — an undertaking in a group containing at least one large undertaking on the qualification date is in scope even if it is individually below the test.

This is a different and higher test than SECR's two-of-three test at £36m turnover, £18m balance sheet total and 250 employees.

Alignment of the ESOS thresholds with SECR was proposed but will not go ahead for Phase 4, and no Phase 5 commitment to it has been published.

Qualification Assessment

Qualification is determined at a single point in time called the 'qualification date'.

For ESOS Phase 4 that date is 31 December 2026 per the ESOS Phase 4 guidance.

Your position on that date fixes your scope for the whole phase, whatever happens before or after it.

For the step-by-step route to the December 2027 deadline, see the full ESOS Phase 4 compliance guide on uksrs.org.uk.

ESOS Phase 4 Timeline

Key Dates

• Compliance Period: 6 December 2023 – 5 December 2027 per GOV.UK ESOS Phase 4 guidance
• Phase 3 Progress Update 2: 5 December 2026 — a live obligation for organisations that notified in Phase 3
• Qualification Date: 31 December 2026
• Compliance (notification) Deadline: 5 December 2027
• Action Plan: 5 December 2028, covering 6 December 2027 – 5 December 2031
• Progress Updates: 5 December 2029, 5 December 2030 and 5 December 2031

These dates are now tabulated explicitly in the Environment Agency’s Phase 4 guidance, published 30 July 2026.

The third progress update is new in Phase 4, added by regulation 28 of SI 2026/701.

The action plan and every progress update need director (or equivalent) sign-off and are submitted through MESOS.

ESOS Compliance Requirements

1. Energy Audits

• Cover at least 95% of total energy consumption — the de minimis was cut from 10% to 5% by SI 2023/1182
• Signed off by a Lead Assessor on a currently approved register
• Cover all four organisational purposes: buildings, industrial processes, transport, and any other purpose not falling within those three
• Identify cost-effective energy efficiency opportunities

2. Alternative Compliance Routes

• ISO 50001: where certification covers total or significant energy consumption, the participant is deemed to have complied with the duties to appoint a lead assessor, carry out the energy audit and produce the ESOS report — a notification of compliance is still required
• Hybrid: partial ISO 50001 coverage exempts only the certified consumption; the remainder needs an ESOS energy audit and a lead assessor

Display Energy Certificates and Green Deal Assessments are removed as ESOS compliance routes: regulation 26 of SI 2026/701omits regulation 34 of the 2014 Regulations, on the Environment Agency’s stated ground that they “provide more limited and less tailored recommendations than an ESOS energy audit”.

Organisations that relied on either in Phase 3 need a full energy audit or expanded ISO 50001 scope.

One further practical point on assessors: the Institution of Chemical Engineers was removed from the list of approved registers for ESOS lead assessors on 16 February 2026, so anyone whose lead assessor was IChemE-registered should confirm their standing on a currently approved register.

3. Responsible Officer Sign-off

• One or more “responsible officers” must be nominated per regulation 30(2) — a director within s.250 Companies Act 2006, or a person exercising management control. “Board level” is guidance shorthand and does not appear in the Regulations
• One responsible officer where the lead assessor is independent of the participant (regulation 30(3)); two in any other case
• Two responsible officers where no lead assessor was appointed — under the 40,000 kWh threshold, or zero energy consumption

ESOS Implementation Steps

Step 1: Determine Qualification

Assess whether your organisation qualifies as at 31 December 2026, testing the corporate group position as well as the individual entity.

Step 2: Deal with any live Phase 3 obligation

If you notified in Phase 3, Progress Update 2 is due by 5 December 2026. There is no penalty for missing it, but the failure is published on the public register.

Step 3: Measure Total Energy Consumption

Calculate your organisation's total energy use across all areas including:

• Buildings (electricity, gas, other fuels)
• Industrial processes
• Transport (company vehicles, business travel)

Step 4: Identify Areas for Energy Audits

Select areas that represent at least 95% of total energy consumption for detailed auditing.

Step 5: Conduct Energy Audits

Engage a Lead Assessor on a currently approved register to sign off the assessment and identify energy saving opportunities.

Step 6: Consider Energy Efficiency Recommendations

Review audit findings and consider implementation of energy efficiency measures.

Step 7: Submit Compliance Notification

Submit compliance notification to the Environment Agency by 5 December 2027, then the Action Plan by 5 December 2028.

Penalties: where they actually bite

ESOS enforcement is asymmetric.

Penalties attach to the compliance-date obligations — up to £50,000 plus up to £40,000 in daily penalties for failure to undertake an assessment — but there is no direct penalty for non-submission of an action plan or a progress update: regulations 34A and 34B are named nowhere in Part 8’s penalty chapter, a genuine statutory gap rather than forbearance.

The primary consequence is publication of the failure on the public register. There is a residual route: an enforcement notice served under regulation 38 requiring an action plan carries the standard penalty (regulation 46(1)) if not complied with — £5,000 plus £500 per working day, capped at 80 working days.

Integration with UK SRS

ESOS compliance can support your UK SRS preparations under UK SRS S2 climate disclosure requirements, particularly for:

• Energy efficiency data: ESOS audits provide baseline energy consumption data
• Scope 1 & 2 emissions: Energy audits help quantify direct and indirect emissions
• Improvement opportunities: Energy efficiency measures support climate transition planning
• Governance structures: Board-level oversight aligns with climate governance requirements

Getting Started

Begin your ESOS Phase 4 compliance preparation by assessing your current energy consumption and identifying approved energy auditors for your sector.

UK SRS Integration GuideAll Compliance Deadlines