The UK Energy Savings Opportunity Scheme: Your 2026 Guide
The Energy Savings Opportunity Scheme (ESOS) is a mandatory energy assessment scheme for large UK organisations.
Introduced under the UK’s implementation of the EU Energy Efficiency Directive, it is designed to help qualifying organisations understand how they use energy across their buildings, industrial processes and transport activities, and identify practical opportunities to reduce energy use, carbon emissions and costs.
How ESOS Works
ESOS operates in four-year compliance periods. Phase 3 covered the period from 6 December 2019 to 5 December 2023, with a qualification date of 31 December 2022 and a final notification of compliance deadline of 5 June 2024.
Most qualifying Phase 3 participants that submitted a notification of compliance and had energy responsibility were also required to submit an action plan and annual progress updates. The Phase 3 action plan deadline was 5 December 2024, the first progress update deadline was 5 December 2025, and the second progress update is due by 5 December 2026.
Phase 4 is now underway
Phase 4 covers 6 December 2023 to 5 December 2027. Its qualification date is 31 December 2026, and the compliance deadline is 5 December 2027.
For Phase 4, qualifying participants will need to complete their assessment and submit their notification of compliance by 5 December 2027. They must then submit an action plan by 5 December 2028, followed by progress updates on 5 December 2029, 5 December 2030 and, under a new requirement, 5 December 2031.
Phase 4 also introduces stronger reporting on implementation. The ESOS report and notification of compliance must include an action plan review, details of energy savings achieved during the compliance period and information about the measures implemented. Participants must also identify measures from the previous action plan that were not implemented and explain why.
ESOS Compliance and Enforcement
Organisations that fail to complete a compliant ESOS assessment and submit a notification of compliance may face enforcement action and civil penalties. For example, failure to undertake an energy audit can result in a fixed penalty of up to £50,000, plus up to £500 for each working day the breach continues after a compliance notice, capped at 80 working days.
ESOS energy audits must be carried out by an approved ESOS Lead Assessor for organisations that qualify under the scheme. ESOS is administered by the Environment Agency, which is also responsible for auditing submissions, carrying out compliance checks and taking enforcement action where necessary.
Who Needs to Comply with ESOS?
ESOS applies to large UK-based organisations and corporate groups if, on the qualification date, it meets either of the following conditions:
- It employs 250 or more people
- It has an annual turnover of more than £44 million and an annual balance sheet total of more than £38 million
Corporate groups may also qualify where at least one of its UK-based subsidiaries meets the above qualification criteria.
Organisations close to the thresholds, or those that have recently grown or reduced in size, should check the detailed rules because ESOS status may depend on whether the organisation has remained above or below the thresholds for two consecutive accounting periods.
What ESOS Means for Large Organisations
For large organisations, ESOS provides a structured opportunity to review energy use and identify where practical improvements can be made.
The assessment should identify tailored and cost-effective measures across buildings, industrial processes and transport. These measures can support lower energy costs, reduced carbon emissions, improved operational efficiency and longer-term decarbonisation plans.
Phase 4 places greater emphasis on accountability and delivery. Participants must report energy savings achieved during the compliance period, describe the measures implemented and review progress against commitments made in their previous action plan.
The ESOS report, notification of compliance, action plan and progress updates require director-level sign-off. Action plans and annual progress updates will be published by the Environment Agency, helping to increase transparency around the measures organisations intend to take and the progress they report.
Although ESOS is not a net zero scheme and does not require every identified recommendation to be implemented, it can support wider energy management, retrofit, carbon reduction and streamlined energy and carbon reporting objectives.
Daniel Pearson, Non-Domestic Team Leader at Elmhurst Energy, said:
ESOS has evolved well beyond a periodic audit exercise. Phase 4 strengthens governance, transparency and accountability, making it an increasingly important driver of long-term energy performance improvement. When integrated into wider energy and retrofit strategies, ESOS can deliver meaningful cost savings, carbon reduction and future regulatory readiness.
Routes to Compliance for ESOS Participants
ESOS participants must cover at least 95% of their total energy consumption through ESOS energy audits, ISO 50001 certification or a combination of eligible routes.
From Phase 4, Display Energy Certificates (DEC) and Green Deal Assessments are no longer accepted as routes to compliance.
Participants that comply solely through ISO 50001 now have reduced obligations where the certification covers all their total energy consumption, or all significant energy consumption as applicable. In these circumstances, they do not need to produce a separate ESOS report or appoint an ESOS Lead Assessor, although they must still submit the required notification through the online MESOS system and meet the relevant sign-off requirements.
ISO 14001 certification is not a standalone deemed compliance route. However, organisations with a certified ISO 14001 environmental management system may use it to support ESOS compliance, for example by integrating ESOS audit activity and evidence into their existing environmental management processes.
Find a qualified ESOS Lead Assessor
Organisations that need support with ESOS should speak to a qualified ESOS Lead Assessor, who can guide them through the assessment process and help ensure the correct energy data, evidence and reporting requirements are addressed.
FIND AN ELMHURST APPROVED ASSESSOR
Opportunities for Energy Professionals
As ESOS remains an important requirement for large UK organisations, there is ongoing demand for competent professionals who can provide high-quality assessment and advisory support. Energy professionals who want to expand their services in this area can develop the required expertise through ESOS Lead Assessor training.
Book an Elmhurst ESOS Lead Assessor Course
Every four years, qualifying large organisations must demonstrate their compliance with the Energy Savings Opportunity Scheme (ESOS). This creates an opportunity for experienced energy professionals working in the non-domestic sector to train as ESOS Lead Assessors and support organisations with their assessments, audits and compliance reporting.
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Sources and further information