The Energy Savings Opportunity Scheme (ESOS) is an energy assessment initiative introduced by the UK government to promote energy efficiency among larger organisations.
Under this scheme, organisations with 250 or more employees, or those meeting specific turnover or balance sheet criteria, have a mandatory requirement to undergo an energy assessment/audit every four years. This audit includes recommendations for energy-saving measures and is required to be verified by a qualified ESOS Lead Assessor.
Although it has long been a staple of the UK’s environmental landscape, regulatory supervision in previous phases has been considered ‘light-touch’. However, recent changes mean oversight has been strengthened with a more measurable framework. For large undertakings in the UK, ESOS Phase 4 represents a significant change from simply identifying energy savings to being held accountable for implementing them.
You must take part in ESOS if your organisation, or any UK undertakings in your organisation’s group, qualifies as a large undertaking on the qualification date.
A large undertaking is any UK undertaking that meets either one or both of the following conditions:
The key qualification date for ESOS Phase 4 is 31 December 2026, with the compliance deadline on 5 December 2027.
One thing to note is that although ESOS reporting is a mandatory requirement when you meet the threshold criteria, it is about much more than just ensuring compliance, and there are a number of additional benefits for businesses, such as:
As the UK government intensifies its focus on achieving net zero emissions, ESOS compliance has become even more crucial.
The key requirements remain unchanged; however, new rules on progress tracking and compliance routes have been introduced. Businesses should act now to stay ahead.
There are a number of changes to ESOS Phase 4, and it’s important to stay informed to ensure you remain compliant. The key changes are:
Display Energy Certificates (DECs) and Green Deal Assessments (GDAs) will no longer be accepted as compliance methods.
Organisations will be required to report progress against their action plan commitments within their ESOS assessments.
These updates aim to provide businesses with adequate time to prepare for significant changes and to assess the impact of recent modifications implemented in Phase 3.
Reports must detail energy savings achieved during the compliance period, categorised by measure and energy-saving type, with combined totals published rather than commercially sensitive individual figures.
There is now a requirement for Lead Assessors to notify their professional body of each ESOS assessment they complete or review. This enables the relevant professional body to carry out quality checks and support greater consistency in ESOS assessments.
Organisations complying fully through ISO 50001 certification covering total or significant energy consumption are exempt from producing a separate ESOS report or appointing a Lead Assessor.
Mandatory net zero requirements have been delayed to Phase 5 (2027–2031), though voluntary reporting using standards such as PAS 51215-1:2025 remains available.
These changes indicate that the ESOS regulations are heading in a new direction, with more focus on accountability through additional requirements such as the need for an action plan and reporting progress disclosures, with the aim of encouraging businesses to move beyond just identifying opportunities and to start demonstrating the energy and carbon savings they have actually achieved.
Previously, ESOS was viewed as simply a compliance exercise. However, the new Phase 4 changes place greater emphasis on turning these recommendations into measurable results.
With the removal of DECs and GDAs as compliance routes, this also suggests that these approaches have not always provided sufficient detail to identify energy-saving opportunities across all operations. As well as this, the introduction of additional quality assurance measures for Lead Assessors should help improve the consistency and quality of assessments being undertaken. This may reflect findings from Environment Agency compliance audits during Phase 3, where some assessments were found not to meet the required standard.
Overall, these changes reinforce the role of ESOS as a tool for driving energy performance improvement, rather than simply achieving compliance.
With the net zero postponement, businesses can now prepare for the anticipated future requirements while ensuring they meet their remaining Phase 3 and Phase 4 obligations without additional pressure.
Companies can use this time to understand the changes, familiarise themselves with how net zero considerations will impact their operations, and integrate long-term sustainability strategies.
By reducing carbon emissions and aligning with the UK’s net zero targets, businesses can anticipate their compliance and benefit from lower energy costs.
Instead of facing immediate regulatory changes, businesses can now focus on meeting ESOS Phase 4 compliance deadlines while strategically incorporating net zero principles at their own pace. This means ensuring they meet the qualification date of 31 December 2026 and submit their compliance reports by 5 December 2027.
Although the Phase 4 compliance deadline in December 2027 feels a long way off, preparing early can provide more time. Early action will help businesses streamline the reporting process and avoid last-minute compliance challenges.
Companies should also consider utilising this time to evaluate their energy efficiency measures and implement cost-effective measures that could reduce their operational expenses.
Investing in energy audits, efficiency technologies and carbon reduction initiatives now can help businesses gain a competitive advantage when Phase 5 mandates are introduced.
If your organisation qualifies for ESOS Phase 4, preparing early can help you understand your requirements and plan for compliance.
We have developed a consultancy service to help fulfil your ESOS compliance requirements.
Find out more about our ESOS support.
Already investing in energy-saving measures? Find out whether your organisation could benefit from our ESOS rebate service.
If you’re unsure whether your business needs to comply, use our ESOS obligation checker.
Alternatively, contact us on 03450 682 572 or email [email protected].
Senior Environmental & Carbon Consultant