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Guidance

Energy savings opportunity scheme (ESOS): find out if you qualify and how to comply

Find out if you qualify for the energy savings opportunity scheme (ESOS) and how to meet the requirements to make your business more energy efficient.

From:
Department for Energy Security and Net Zero, Environment Agency and Department for Business, Energy & Industrial Strategy
Published:
26 June 2014
Last updated:
2 September 2026 — See all updates

The energy savings opportunity scheme (ESOS) is a mandatory energy assessment scheme for organisations in the UK that meet the qualification criteria.

Organisations that qualify for ESOS must carry out an assessment every 4 years. The assessment includes an audit of the energy used by their buildings, industrial processes and transport.

The ESOS assessment is designed to identify tailored and cost-effective measures that allow participating businesses to save energy and achieve carbon and cost savings. The costs of an ESOS assessment are estimated to be significantly outweighed by the savings from implementing the recommendations.

For full details of how to comply with ESOS requirements see:

This guidance works alongside the legislation to help you understand the requirements of the scheme.

ESOS latest updates

Phase 4 changes

The government has amended the Energy Savings Opportunity Scheme Regulations 2014 ahead of the fourth compliance period, also known as ESOS phase 4. This means that:

  • you can no longer use Display Energy Certificates (DECs) and Green Deal assessments (GDAs) as alternative compliance routes
  • progress against action plan commitments must be included in your ESOS assessment
  • you must provide an explanation where action plan commitments have not been met

Net zero assessments

Participants in phase 4 can voluntarily include net zero considerations in their ESOS assessment using the following British Standards Institution (BSI) standards:

These standards combine the process and lead assessor competence standards required for the mandatory energy assessment for ESOS and a decarbonisation assessment.

The existing competency standard, PAS 51215:2014 Energy efficiency assessment: Competence of a lead energy assessor, remains the competency standard for ESOS lead assessors.

Manage your Energy Savings Opportunity Scheme Reporting (MESOS) is the online system for reporting compliance with the ESOS requirements. MESOS does not allow reporting of any voluntary decarbonisation assessments, although the Department for Energy Security and Net Zero (DESNZ) is considering this for potential future changes to the online system. Organisations may wish to publish this information via their own reports or websites. 

Reminder: Phase 3 requirements

If you qualified for ESOS in the third compliance period, also known as ESOS phase 3, between 6 December 2019 and 5 December 2023, an annual progress update is due to be submitted by 5 December 2026 in relation to the action plan you submitted. 

The progress update must be signed off by a board level director (or equivalent) and submitted via MESOS.

For full details of how to complete ESOS annual progress updates, see section 14 of the guidance on how to comply with ESOS phase 4.

If you have not yet submitted an action plan you should contact the Environment Agency.

Find out if you qualify for ESOS phase 4 

ESOS applies to large UK undertakings and their corporate groups. It mainly affects businesses but can also apply to not-for-profit bodies and any other non-public sector undertakings that are large enough to meet the qualification criteria.

Your organisation qualifies for ESOS phase 4 if, on 31 December 2026, it meets the ESOS definition of a large undertaking.

The deadline for submitting a notification of compliance for phase 4 of ESOS is 5 December 2027.

Organisations that qualify for ESOS must comply with their ESOS obligations, via MESOS.

For phase 3, the qualification date was 31 December 2022.

Corporate groups qualify if at least one UK group member meets the ESOS definition of a large undertaking.

UK registered establishments of an overseas company also need to take part in ESOS (regardless of their size) if any other part of their global corporate group activities in the UK meet the ESOS qualifying criteria.

For organisations very close to the qualification threshold or which have substantially increased or decreased in size in recent years, see section 1.6 of the guidance on how to comply with ESOS phase 4. This includes additional information on how to assess if you qualify.

Public sector organisations do not usually need to comply with ESOS. For more information on organisations that do not need to comply, see section 1.2 of the guidance on how to comply with ESOS phase 4.

Large undertakings

For ESOS phase 4, a large undertaking is any UK company that either:

  • employs 250 or more people, or
  • has an annual turnover in excess of £44 million, and an annual balance sheet total in excess of £38 million

A person is employed by an undertaking if they are:

  • an employee
  • an owner or manager
  • a partner

An ‘employee’ is a person employed under contracts of service. Their contracted hours and status (full time or part time) are irrelevant to their classification as an employee.

For further guidance on who qualifies, see section 1 of the guidance on how to comply with ESOS phase 4.

If you do not qualify for ESOS phase 4

If you have previously been contacted by your regulator, or you qualified for any previous phases but not for phase 4, you need to tell your regulator you do not qualify.

ESOS regulation and penalties

Your ESOS regulator is responsible for compliance and enforcement activities. It may issue civil sanctions including financial penalties if an organisation does not meet the scheme’s obligations.

Read the Environment Agency’s approach to ESOS regulation and penalties in their enforcement and sanctions policy (annex 2, section D). Other scheme regulators apply a similar approach - see section 15 of the guidance on how to comply with ESOS phase 4.

A summary of the penalties imposed in England is available.

Complete an ESOS assessment

For full details of how to comply with phase 4 ESOS requirements, see:

Summary of the steps required to complete an ESOS assessment

1. Calculate your total energy consumption

This is the energy used by assets held or activities carried out by your organisation or group. This includes the energy consumed by buildings, industrial processes and transport.

2. Identify your areas of significant energy consumption

This is the energy used by assets held, or activities carried out, by your organisation that needs to be included in an energy audit or covered by another route to compliance (see step 4) and must account for at least 95% of your total energy consumption.

3. Calculate your energy intensity ratios

You must calculate energy intensity ratios for each of:

  • buildings
  • transport
  • industrial processes
  • other energy uses outside of these

An energy intensity ratio is a measurement which relates an organisation’s consumption to an appropriate indicator activity. This allows comparison of energy efficiency performance over time.

For full details on calculating energy intensity ratios, see section 6 of the guidance on how to comply with ESOS phase 4.

We recommend the approach set out in the full guidance, but the legal requirement is that the indicator for each organisational purpose is: 

  • quantifiable
  • associated with the assets or activities that relate to the specific organisational purpose
  • calculated using verifiable data where reasonably practicable or a reasonable estimate (from phase 4 onwards)

You should explain the approach you have taken in your compliance notification, if it differs from the one suggested in guidance. You should also keep a record of the approach you have taken in your evidence pack.

4. Decide on your routes to compliance and appoint a lead assessor

You must comply using an energy audit or an ISO 50001 certification to cover all areas of either significant energy consumption or total energy consumption (as applicable).  From phase 4 onwards, DECs and GDAs can no longer be used as alternative compliance routes.

If complying with ISO 50001, the certification must have been issued after 5 December 2023 and be valid at the compliance date, 5 December 2027.

You need to have your ESOS assessment signed off by an ESOS lead assessor unless:

  • your total energy consumption is covered by an ISO 50001 certification or is less than 40,000 kWh
  • your significant energy consumption is covered by an ISO 50001 certification, from phase 4 onwards

For guidance on appointing a lead assessor and using the ISO 50001 alternative compliance route, see sections 7 and 9 in the guidance on how to comply with ESOS phase 4.

5. Carry out any necessary ESOS energy audits

An ESOS compliant energy audit must meet these criteria:

  • it must be based, so far as reasonably practicable, on verifiable energy consumption data measured over a 12-month period, which begins no earlier than 6 December 2022 for phase 4
  • the 12-month period must begin no earlier than 24 months before the start of the ESOS energy audit
  • it must analyse the participant’s energy consumption and energy efficiency
  • it must identify energy saving opportunities
  • it must include site visits

For guidance on carrying out an ESOS energy audit, see section 8 of the guidance on how to comply with ESOS phase 4.

6. Complete the ESOS report and share with the corporate group

You must complete an ESOS report detailing your ESOS assessment (an audit only, or a combination of an audit and ISO 50001 certification if the ISO 50001 certification does not cover the significant or total energy consumption), unless you have zero energy supplies.

The ESOS report is a record of your assessment and includes:

  • information about the energy audit and any ISO 50001 certification used in addition to it, and what they cover
  • the energy saving opportunities identified
  • the energy savings achieved since the previous ESOS compliance date

If you comply exclusively using an ISO 50001 certification to cover either the significant or total energy consumption, an ESOS report is not required.

From phase 4 onwards, additional detail must be provided on the energy savings achieved, and the action plan must be reviewed to identify any measures in it that were not implemented and an explanation provided of the reasons why.

If your organisation is part of a corporate group, you must provide relevant information from the ESOS report to all members of the corporate group.

For more detail of the specific requirements for an ESOS report, see section 10 in the guidance on how to comply with ESOS phase 4.

7. Notification of compliance

You must submit a notification of compliance using MESOS.

The notification includes:

  • details about your organisation
  • how it has complied
  • energy consumption information
  • energy savings opportunities that have been identified

The deadline for submitting a compliance notification for phase 4 is 5 December 2027.

Before submitting the compliance notification, you must get sign off on both the ESOS assessment and the content of the compliance notification from one board level director, or a person exercising management control from one of the undertakings in the participant group.

See section 12 of the guidance on how to comply with ESOS phase 4 for more details on sign-off.

You should use MESOS to complete your notification of compliance. You will be able to create a GOV.UK One Login to sign in to MESOS. You can partially complete your notification and save it for submitting later.

Start your notification of compliance now

The scheme administrator will publish the majority of the information in your compliance notification, with the exception of personal or commercially sensitive details and feedback. Appendix B of the guidance on how to comply with ESOS phase 4 provides details of the information that will be published.

8. Evidence pack

You need to keep records of how you have complied with ESOS in an evidence pack.

For details of what you must include in your evidence pack, see section 11 of the guidance on how to comply with ESOS phase 4.

Approved registers for ESOS lead assessors

If you want to become a lead assessor, you have to be a member of an approved professional body register. Individuals cannot apply directly to the Environment Agency to be approved.

You can contact the approved organisations listed for further information about the application processes or approved lead assessors on their registers.

You must appoint a lead assessor from this list, or your energy audit will not be considered as complying with the regulations:

Published data

The Environment Agency publishes the data provided by organisations that submitted a notification of compliance in previous phases of ESOS. This data is published to meet the Environment Agency’s statutory responsibility under the Energy Savings Opportunity Scheme Regulations 2014 and in alignment with government open data policies.

The published data:

  • shows the information on existing requirements that are published by the scheme administrator, as detailed in appendix B of the guidance on how to comply with ESOS phase 4
  • does not include personal data – this is protected under the General Data Protection Regulation 2018 (GDPR)
  • contains no amendments – unless requested or to remove personal data
  • has not been verified for compliance – it is a record of notifications

Some organisations within a group may be covered by a notification of a UK parent and may not be readily identifiable.

UK regulators

The UK regulators are:

  • Environment Agency for organisations whose registered office is in England
  • Natural Resources Wales for organisations whose registered office is in Wales
  • Northern Ireland Environment Agency for organisations whose registered office is in Northern Ireland
  • Scottish Environment Protection Agency for organisations whose registered office is in Scotland
  • Secretary of State for Department for Energy Security and Net Zero for organisations whose activities consist wholly or mainly of offshore activities

Contact details

For more information on ESOS, email esos@environment-agency.gov.uk. The Environment Agency will respond within 10 working days. Send your queries well in advance of the compliance deadline to ensure you have enough time to fulfil your obligations before submitting your notification of compliance.

For queries on the MESOS reporting system, email esos-it@environment-agency.gov.uk.

For offshore related queries, email OPRED@energysecurity.gov.uk.

Updates to this page

Published 26 June 2014
Last updated 2 September 2026 Show all updates

  1. Requirements for compliance with the energy savings opportunity scheme (ESOS) have been updated for phase 4.

  2. Removed the Institution of Chemical Engineers from the list of approved registers for ESOS lead assessors.

  3. Section 'List of approved registers for ESOS lead assessors' added information for Quidos 'ESOS register, ESOS lead assessor certification'.

  4. Removed Stroma Certification Ltd from the list of approved registers for ESOS lead assessors.

  5. Added information on phase 4 changes, and updated details on how to submit an action plan via the Manage your ESOS reporting system. Action plans can still be submitted until 5 March 2025.

  6. The extension to the deadline for submitting notifications of compliance for phase 3 of ESOS has now passed.

  7. If your organisation qualifies for ESOS Phase 3 but has not yet submitted a notification of compliance, you need to do so by 6 August 2024.

  8. The Manage your Energy Savings Opportunity Scheme (MESOS) system is now available to complete your notifications of compliance.

  9. The Manage your Energy Savings Opportunity Scheme (MESOS) system is now available for you to register your Phase 3 user and organisational accounts.

  10. Guidance updated to reflect the changes for Phase 3.

  11. Removed 'ECMK Limited – ECMK ESOS lead assessor register' from the list of Approved registers of ESOS lead assessors as they are no longer taking part in the scheme.

  12. Added what a 'large undertaking' is defined as for the qualification date for the third ESOS compliance period, which will be 31 December 2022.

  13. Added information about ESOS phase 2.

  14. Added under section: ESOS regulation and penalties 'We publish a summary of the penalties imposed on data.gov.uk'.

  15. Updated link to The Institute of Environmental Management and Assessment to: https://www.iema.net/specialist-registers/join-esos/iema-esos-lead-assessor-register.

  16. Update to the ESOS compliance dataset. Removal of ‘intend to comply’ information as this is no longer relevant.

  17. This update is to reflect the latest position on ESOS notifications up to 31 January 2017.

  18. Section 'ESOS published data': data published on data.gov.uk provided by the organisations that submitted an intent to comply notification by 25 August 2016.

  19. Section 'ESOS published data': See the published data provided by the organisations that submitted a notification of compliance by 30 June 2016.

  20. New section 'ESOS published data'.

  21. If you qualify for ESOS you should have submitted your notification of compliance by 5 December 2015. Submit your notification as soon as possible if you haven’t done so already.

  22. You must inform the Environment Agency by 5 December 2015 if you cannot submit a notification of compliance, using the online form.

  23. Text updated to reflect the Environment Agency's amended Enforcement and Sanctions Guidance.

  24. ESOS workshop dates and venues announced for March 2015.

  25. Exchange rate figures added for pound sterling for the first compliance period based on the Bank of England daily spot exchange rate on 31 December 2014 (the qualification date).

  26. Updated list of approved registers. Text amended to reflect that the application process for registers is now closed.

  27. Page updated with: * the link to the online notification system * the list of approved lead assessors

  28. Update to the application process for registering qualified energy professionals to act as lead assessors for ESOS.

  29. First published.

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