ESOS Phase 4 deadline — 5 December 2027
The ESOS Phase 4 compliance deadline is 5 December 20271.
All qualifying organisations must complete their energy audits, develop action plans, and obtain board-level sign-off by this date.
Unlike previous phases, there is no separate notification deadline — compliance is confirmed through the ongoing ESOS notification process with the Environment Agency4.
The qualification assessment period runs from 1 January 2023 to 31 December 2026 (4 years), with qualification status determined at the single point-in-time of 31 December 20261.
ESOS has operated on 4-year cycles since inception: Phase 1 (2015), Phase 2 (2019), Phase 3 (2023), and Phase 4 (2027)1.
ESOS Phase 4 requirements and qualification criteria
The core **ESOS Phase 4 requirements** are to assess total energy consumption, conduct energy audits covering at least 95% of that energy, set out an action plan, and obtain board-level sign-off before the deadline1.
The full **ESOS qualification criteria** are set out in our ESOS Phase 4 qualification guide.
An organisation qualifies for ESOS Phase 4 if its UK group meets specific size criteria at 31 December 20261.
The qualification test uses the "large undertaking" definition from the Companies Act 2006, with qualification requiring EITHER the employee test OR both financial tests together1.
Employee test: 250 or more employees in the UK at 31 December 2026.
This alone qualifies the organisation, regardless of financial position1.
Financial tests (both required): Annual turnover of £44 million or more AND balance sheet total of £38 million or more.
Both thresholds must be exceeded — meeting only one financial test is insufficient for qualification1.
These figures represent the UK equivalents of the EU thresholds (€50m/€43m) applied at current exchange rates3.
Group aggregation rules apply where organisations are part of larger corporate groups.
All UK group companies' figures are aggregated when determining qualification, with the ultimate parent undertaking responsible for compliance1.
ESOS Phase 4 key changes from Phase 3
ESOS Phase 4 introduces significant changes from Phase 3, primarily through the Energy Savings Opportunity Scheme (Amendment) Regulations 2023 (SI 2023/1182)2.
The most substantial changes relate to action plan requirements, compliance routes, and enforcement mechanisms.
Mandatory action plans are the key Phase 4 requirement.
Part 6A of SI 2023/1182 requires all qualifying organisations to develop action plans identifying energy efficiency measures and implementation timelines2.
Action plans must receive board-level approval and include annual progress updates.
Compliance route changes include removal of the display energy certificate (DEC) and green deal assessment routes that were available in earlier phases2.
Phase 4 compliance routes are: (1) ESOS energy audit, (2) ISO 50001 certification covering 100% UK energy consumption2.
Lead assessor requirements have been enhanced, with stricter continuing professional development obligations and updated competency frameworks3.
All energy audits must be conducted by certified lead assessors meeting the revised standards.
Net zero requirements originally planned for Phase 4 have been deferred to Phase 5, allowing organisations additional time to develop comprehensive decarbonisation strategies3.
Energy audit requirements
ESOS energy audits must cover 95% of the organisation's total UK energy consumption3.
This includes all energy types: electricity, gas, transport fuels, and other energy sources.
The 5% de minimis threshold allows exclusion of minor energy uses that would be disproportionately expensive to audit.
Audit scope covers all UK activities of the qualifying group, including buildings, industrial processes, and transport.
Energy audits must identify opportunities for energy efficiency improvements and provide cost-benefit analysis of recommended measures3.
Data requirements include 12 months of energy consumption data, covering the period most representative of normal operations.
Where COVID-19 or other exceptional circumstances affected energy use, adjustments may be made with Environment Agency guidance4.
- Energy consumption data for all UK sites and activities
- Analysis of energy efficiency opportunities with cost-benefit assessment
- Recommendations prioritised by payback period and energy savings potential
- Board-approved action plan identifying implementation measures and timelines
Compliance routes
ESOS Phase 4 offers two primary compliance routes2:
Route 1: ESOS energy audit conducted by a certified lead assessor, covering 95% of UK energy consumption.
This is the standard compliance route for most organisations3.
Route 2: ISO 50001 certification covering 100% of the organisation's UK energy consumption.
ISO 50001 provides an alternative compliance route where the energy management system meets ESOS requirements2.
Penalties for non-compliance
ESOS enforcement operates through civil sanctions under the Regulatory Enforcement and Sanctions Act 20086.
The Environment Agency (and equivalent regulators in devolved nations) applies a structured penalty framework based on the nature and extent of non-compliance4.
Maximum penalties are £45,000 for failure to notify compliance and £90,000 for failure to undertake an energy audit4.
Penalty levels depend on organisation size, compliance history, and cooperation with enforcement activities.
Publication of non-compliance on the Environment Agency's public register is standard practice, serving as additional reputational consequence beyond financial penalties4.
This publication remains accessible to stakeholders conducting due diligence on sustainability compliance.
Action plan requirements
Action plans are mandatory for ESOS Phase 4 under Part 6A of SI 2023/11822.
Action plans must identify specific energy efficiency measures, implementation timelines, and resource requirements for delivering identified opportunities.
Board approval is required for all action plans, ensuring senior-level commitment to energy efficiency implementation2.
Action plans must be signed off by a board director or equivalent senior officer.
Annual progress updates must be submitted to demonstrate implementation progress against action plan commitments2.
Updates should quantify energy savings achieved and explain any deviations from planned implementation.
- Specific energy efficiency measures with quantified savings potential
- Implementation timelines and resource allocation
- Board-level approval and senior management commitment
- Annual progress reporting against action plan commitments
What is the ESOS Phase 4 deadline?
ESOS Phase 4 compliance deadline is 5 December 2027. All energy audits, action plans, and board-level sign-off must be completed by this date. There is no separate notification deadline — compliance is confirmed through the ESOS notification process.
What are the qualification criteria for ESOS Phase 4?
ESOS Phase 4 qualification is assessed at 31 December 2026. A UK group qualifies if it meets EITHER: (1) 250+ employees in the UK, OR (2) BOTH £44m+ annual turnover AND £38m+ balance sheet total. Meeting only one financial test is insufficient.
What are the penalties for ESOS Phase 4 non-compliance?
Civil penalties under the Regulatory Enforcement and Sanctions Act 2008: up to £45,000 for failure to notify compliance, up to £90,000 for failure to undertake energy audit. Penalties may include publication on the Environment Agency public register.
What changed from Phase 3 to Phase 4?
Key changes include: mandatory action plans (Part 6A SI 2023/1182), annual progress updates, removal of display energy certificate route, enhanced lead assessor requirements, and deferral of net zero requirements to Phase 5.
Can ISO 50001 be used for ESOS Phase 4 compliance?
Yes. ISO 50001 energy management certification covering 100% of the organisation's UK energy consumption provides an alternative compliance route to the standard ESOS energy audit.
