Energy Savings Opportunity Scheme
ESOS is a UK mandatory energy assessment scheme for large undertakings. Phase 4 requires qualifying organisations to audit at least 95% of their energy consumption across buildings, transport and industrial processes, identify cost-effective savings, have the assessment signed off by an approved ESOS Lead Assessor, and notify the Environment Agency through the MESOS reporting system by 5 December 2027. An action plan and two annual progress updates then follow.
Who needs to comply
Large UK undertakings: 250+ employees, or £44m+ turnover and £38m+ balance sheet, measured on the 31 December 2026 qualification date
250+ employees
Any UK undertaking employing 250 or more people on the qualification date
£44m+ turnover AND £38m+ balance sheet
Smaller headcount but meeting both financial thresholds
Corporate groups
If the highest UK parent qualifies, the whole group is in scope
Either the employee threshold OR both financial thresholds must be met on the 31 December 2026 qualification date.
What's required
The key disclosure and reporting requirements under ESOS.
Energy audit covering at least 95% of total energy consumption, known as your areas of significant energy consumption (AoSEC)
12 months of energy data spanning buildings, transport and industrial processes, including the qualification date
Identification of cost-effective energy saving opportunities
Sign-off by an approved ESOS Lead Assessor
Notification of compliance to the Environment Agency via the MESOS reporting system by 5 December 2027
An ESOS action plan with board-level director sign-off, followed by two annual progress updates
How Climatise automates ESOS compliance
From raw data to audit-ready report, fully automated.
Complete Energy Mapping
Automatically categorise total energy consumption across buildings, transport and processes, and surface your areas of significant energy consumption (AoSEC).
Savings Identification
AI-powered analysis identifies the most cost-effective energy efficiency opportunities across your portfolio.
Assessor-Ready Evidence Pack
Auto-assemble the reports, energy data, and sign-offs your Lead Assessor needs for MESOS notification.
Action Plan & Progress Tracking
Carry recommendations into an action plan and track delivery through the annual progress updates Phase 4 now requires.
Frequently asked questions
The Energy Savings Opportunity Scheme is a UK government scheme that requires large enterprises to audit the energy used by their buildings, industrial processes, and transport, and to identify cost-effective energy saving measures. It runs in four-year compliance phases.
The Phase 4 qualification date is 31 December 2026 and the notification of compliance deadline is 5 December 2027. Your assessment must be signed off by an approved ESOS Lead Assessor and submitted via the MESOS reporting system by that date.
Large undertakings in the UK: any organisation with 250+ employees, or with annual turnover exceeding £44m AND a balance sheet exceeding £38m, measured on the 31 December 2026 qualification date. If the highest UK parent company qualifies, all UK group companies are in scope.
From Phase 3 onwards, ESOS participants must submit an action plan setting out the energy-saving measures they intend to implement, signed off by a board-level director and submitted via MESOS. It is followed by two annual progress updates reporting what has been delivered. ESOS is now an ongoing cycle, not a one-off audit.
Climatise ingests your energy data, maps it to your sites and areas of significant energy consumption, identifies cost-effective opportunities, and assembles an assessor-ready evidence pack for MESOS notification. It then carries those recommendations into the action plan and progress updates. The same dataset also feeds SECR and UK SRS.
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