Energy Savings Opportunity Scheme (ESOS)

ESOS latest updates

Phase 4 changes

The following changes announced in the previous government’s response to the ESOS consultation will not go ahead for Phase 4:

• changes to refocus the scheme to cover net zero as well as energy efficiency (responses to questions 16, 17, 18 and 19)
• change to qualification thresholds to better align with Streamlined Energy and Carbon Reporting (SECR) (response to question 23)

Following delays to the introduction of Phase 3 legislation and guidance, and in order to give sufficient time for such a major change to ESOS, the new government has decided to postpone the introduction of net zero requirements until Phase 5.

The following changes announced in the previous government’s response to the ESOS consultation are intended to go ahead for Phase 4, subject to parliamentary time and scrutiny:

• removal of Display Energy Certificates (DECs) and Green Deal Assessments (GDAs) as compliance routes (response to question 10)
• progress against action plan commitments to be included in the ESOS assessment (response to question 20)
• where action plan commitments have not been met, participants must provide an explanation (response to question 20)

Further details of these changes will be provided in due course. These changes and full guidance, as well as the necessary changes to the Manage your ESOS reporting system are planned to be in place by early 2027 in advance of the notification of compliance deadline for Phase 4, which is 5 December 2027.

Publication of new PAS standards

On 7 February the British Standards Institution (BSI) published two new standards which were referenced in the government response to the ESOS consultation:

• PAS 51215-1:2025 Energy and decarbonization assessment – Part 1: Process – Specification
• PAS 51215-2:2025 Energy and decarbonization assessment – Part 2: Competencies of lead assessors and assessment teams – Specification

Participants will be able to use these standards on a voluntary basis for ESOS compliance. Further guidance on voluntary use of these standards will be published in due course.

The existing competency standard, PAS 51215:2014 Energy efficiency assessment: Competence of a lead energy assessor – Specification, will continue to be used as the competency standard for ESOS lead assessors for Phase 4.

The new PAS 51215-2:2025 competency standard can be used on a voluntary basis by organisations wanting to determine whether an assessor is suitable to carry out an assessment according to PAS 51215-1:2025.

ESOS action plan

If you were required to submit a notification of compliance for the third compliance period (deadline 5 June 2024), you must also submit an action plan and progress updates during the subsequent relevant compliance period.  If you did not qualify for ESOS for the third compliance period, you do not need to complete an action plan or progress updates in the subsequent compliance period.

For details about ESOS action plans, see Section 12 in the full guidance.

The action plan must be signed off by a board level director (or equivalent), and submitted via the Manage your ESOS reporting system by the action plan deadline. For the third compliance period this deadline was 5 December 2024, which has now passed.

If you have not yet submitted an action plan, you can still submit this using the Manage your ESOS reporting system. No remedial actions will be considered for action plans submitted up until 5 March 2025.

Start your action plan now

Annual progress updates

Following submission of the action plan, you must submit an annual progress update against your action plan commitments in the 2 subsequent years.

The deadline for submitting an annual progress update is 12 months after the action plan deadline, and then 12 months after the submission deadline for the first progress update. For the third compliance period, the deadlines are 5 December 2025 and 5 December 2026.

The progress update must be signed off by a board level director (or equivalent), and submitted via the Manage your ESOS reporting system.

For full details of ESOS annual progress updates, see Section 13 of the guidance.

About the Energy Savings Opportunity Scheme (ESOS)

ESOS is a mandatory energy assessment scheme for organisations in the UK that meet the qualification criteria. The Environment Agency is the UK scheme administrator.

Organisations that qualify for ESOS must carry out ESOS assessments every 4 years. These assessments are audits of the energy used by their buildings, industrial processes and transport.

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

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

• the Energy Savings Opportunities Scheme Regulations 2014 as amended most recently by the Energy Savings Opportunities Scheme (Amendment) Regulations 2023,
• the Phase 3 guidance. We will update this guidance for Phase 4.

The guidance works alongside the legislation to help participants understand the requirements, but the ultimate source of ESOS requirements is the legislation.

Find out if you qualify for ESOS phase 3

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 qualified for the third compliance period (ESOS phase 3) if, on 31 December 2022, it met the ESOS definition of a large undertaking.

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 will 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, read the full guidance on complying with ESOS. 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 full guidance on complying with ESOS

Large undertakings

For the qualification date for the third compliance period of ESOS (31 December 2022) 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 for ESOS, see section 1 in the full guidance.

Deadlines for ESOS compliance

Organisations that qualify for ESOS must notify the Environment Agency by a set deadline that they have complied with their ESOS obligations.

The deadline for submitting a notification of compliance for phase 3 of ESOS was 5 June 2024.

Any organisation that qualified for phase 3 of ESOS and has failed to submit a notification of compliance is now at risk of enforcement action and should contact the Environment Agency immediately.

The qualification thresholds and date for phase 3 have not been changed; phase 3 of ESOS still applies to all organisations (and their corporate groups) that were classed as large undertakings on 31 December 2022.

Organisations that qualified for ESOS in Phase 3 will be required to comply with the Energy Savings Opportunities Scheme (Amendment) Regulations 2023.

Changes include:

• standardization through strengthening requirements for audits
• all participants are now expected to produce an ESOS report, action plan and annual progress reports
• participants will now also be required to publicly disclose high level recommendations

ESOS regulation and penalties

Your environmental 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 full guidance.

A summary of the penalties imposed is available on data.gov.uk.

If you do not qualify for ESOS phase 3

If you have been contacted by the Environment Agency in the past, or you qualified for phase 1 and/or phase 2 but not for phase 3, you need to tell the Environment Agency you do not qualify.

Complete an ESOS assessment

Completing an ESOS assessment now has additional requirements, in line with the 2023 regulations.

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

• the Energy Savings Opportunities Scheme Regulations 2014 as amended most recently by the Energy Savings Opportunities Scheme (Amendment) Regulations 2023,
• the Phase 3 guidance. We will update this guidance for Phase 4

The guidance works alongside the legislation to help participants understand the requirements, but the ultimate source of ESOS requirements is the legislation.

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 4 below) 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 the above 3

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 in the full guidance.

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

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 route(s) to compliance and appoint a lead assessor

You must choose one or more routes to compliance, ensuring all areas of either significant or total consumption (as appropriate) are covered.

If complying with ISO 50001, display energy certificates and/or green deal assessments, it must have been issued after 5 December 2019 and be valid at either the original compliance date (5 December 2023) or the extended compliance date (5 June 2024).

All participants need to have their ESOS assessment signed off by an ESOS lead assessor, unless 100% of your energy supplies are covered by ISO 50001,  or your total energy consumption is less than 40,000 kWh.  

For guidance on appointing a lead assessor and using an alternative compliance route, see Sections 7 and 9 in the full guidance.

5. Carry out any necessary ESOS energy audits

An ESOS compliant energy audit must meet these criteria:

• it must be based on 12 months’ verifiable data, beginning no early than 6 December 2018 for the phase 3 compliance period
• 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 in the full guidance.

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

You must complete an ESOS report detailing your ESOS assessment (audit or alternative compliance route), unless you have zero energy supplies.

The ESOS report is a record of your assessment and includes information about the compliance route used and what it covers, the energy saving opportunities identified and energy savings achieved since the previous ESOS compliance date.

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, as detailed in the Energy Savings Opportunities Scheme (Amendment) Regulations 2023.

For more detail of the specific requirements for an ESOS report, see section 10 in the full guidance.

7. Notify the Environment Agency

When you have undertaken an ESOS assessment and are compliant with your obligations, you must submit a notification of compliance using the Managing your ESOS system.

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 the third compliance period was 5 June 2024.

Any organisation that qualified for phase 3 of ESOS and has failed to submit a notification of compliance is now at risk of enforcement action and should contact the Environment Agency immediately.

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

See section 11 in the full guidance for more details on Director sign-off.

Use the Managing your ESOS (MESOS) system to complete your notification of compliance

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 full guidance 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 14 of the full guidance.

List of approved registers for ESOS lead assessors

• Association of Energy Engineers – certified energy auditor international or certified energy manager international
• CIBSE (The Chartered Institution of Building Services Engineers) – CIBSE low carbon consultant (LCC) register, ESOS lead assessor subset
• Elmhurst Energy Systems – Elmhurst approved ESOS lead assessor
• Energy Institute – chartered energy manager, register of professional energy consultants
• Energy Managers Association – EMA energy saving opportunity scheme lead assessor register
• InstitutionThe of Chemical Engineers – register of chartered chemical engineers (MIChemE/FIChemE) ESOS LEA
• Institute of EnvironmentalSustainability Management and AssessmentEnvironmental Professionals – register of IEMAISEP members who can act as third-party lead assessors
• Quidos – ESOS register, ESOS lead assessor certification

If you want to become a lead assessor, you have to be (or become) 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 here for further information about the application processes or approved lead assessors on their registers.

ESOS: published data

Notification of compliance data

The Environment Agency publishes the data provided by organisations that submitted a notification of compliance in phases 1 and 2 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 full guidance on complying with ESOS
• does not include personal data – this is protected under the General Data Protection Regulation 2018
• 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.

More information about ESOS

The introduction of ESOS in 2014 addressed a finding in the 2012 UK Energy Efficiency Strategy that lack of information was a key barrier to the uptake of energy efficiency measures by business.

Government established ESOS to implement Article 8 (4 to 6) of the EU Energy Efficiency Directive (2012/27/EU). The ESOS Regulations 2014 give effect to the scheme.

The current high cost of energy and the UK’s net zero legislation has made it more important to help businesses reduce their energy and emissions since leaving the EU. A Post Implementation Review of ESOS in 2020 found businesses were unlikely to carry out energy audits unless mandated to do so, which makes ESOS an important lever in encouraging energy efficiency in business.

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.