How to prepare your business for an ESOS assessment
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The Energy Savings Opportunity Scheme (ESOS) is a mandatory energy assessment scheme for qualifying UK organisations. It requires businesses to assess energy consumption and identify opportunities to improve energy efficiency.
For ESOS Phase 4, the qualification date is 31 December 2026, with a compliance deadline of 5 December 2027. Starting early gives organisations time to review their obligations, organise information and address gaps before submitting their assessment.
An ESOS assessment examines how energy is consumed across a qualifying organisation and identifies opportunities to improve energy efficiency.
The assessment process involves calculating total energy consumption, identifying significant energy consumption and determining how that energy use will be covered by an appropriate compliance route.
Where energy audits are required, they must identify practical energy-saving opportunities based on the organisation's activities.
ESOS operates on a four-year cycle, although the specific requirements can change between compliance periods.
For Phase 4, businesses must also address additional requirements relating to energy savings, energy intensity ratios and progress against previous action plan commitments.
ESOS applies to large UK undertakings and qualifying corporate groups.
For Phase 4, an undertaking generally qualifies if it meets either of the following criteria:
Corporate groups can also qualify where at least one UK group member meets the definition of a large undertaking.
The Phase 4 qualification date is 31 December 2026.
Businesses approaching these thresholds should review the detailed qualification rules, particularly where organisational structures or employee numbers have changed.
The ESOS Phase 4 compliance deadline is 5 December 2027.
Qualifying organisations must complete the necessary assessment requirements and submit their notification of compliance by this date.
Businesses that participated in earlier phases should also consider any outstanding obligations relating to their previous ESOS action plans.
For example, the final Phase 3 annual progress update is due by 5 December 2026 for organisations subject to that requirement.
Planning ahead is important because gathering energy records, arranging site visits and completing internal reviews can take time.
Preparation is easier when the process is divided into manageable stages.
Start by establishing which parts of your organisation must be included.
This may involve reviewing corporate group structures, business activities, sites and assets.
Businesses should identify which entities fall within the ESOS assessment and ensure that relevant energy consumption is captured.
Where several organisations form part of a qualifying corporate group, responsibilities should be agreed early to avoid gaps or duplication.
ESOS preparation often requires information from several departments.
Finance teams may hold energy invoices, facilities teams may manage building consumption, and operations teams may have records relating to transport or industrial processes.
Assign responsibility for collecting and checking each type of information.
It is also important to identify who will oversee the assessment, communicate with external specialists and coordinate the final approval process.
Businesses must calculate total energy consumption across relevant assets and activities.
Useful information may include:
Information should be consistent, sufficiently detailed and appropriate to the reporting period.
Businesses should identify missing records early rather than waiting until the assessment is underway.
Once total energy consumption has been calculated, the organisation must identify its areas of significant energy consumption.
For ESOS Phase 4, significant energy consumption must account for at least 95% of the organisation's total energy consumption.
This energy use must be covered by an appropriate compliance route.
For businesses operating multiple sites or energy-intensive processes, breaking consumption down by activity can help establish which areas require further assessment.
The remaining consumption must still be included when calculating the organisation's total energy use.
ESOS Phase 4 requires qualifying organisations to calculate energy intensity ratios for relevant energy uses.
An energy intensity ratio compares energy consumption against an appropriate measure of activity.
For example, a business might compare building energy consumption against floor area or industrial energy consumption against production output.
The chosen measure should be relevant to the activity and supported by reliable information.
Businesses should prepare suitable activity data alongside their energy consumption records so these calculations can be completed consistently.
Businesses must establish how they will meet their ESOS assessment obligations.
Phase 4 compliance routes include ESOS-compliant energy audits and qualifying ISO 50001 certification, or an appropriate combination.
ISO 50001 is an international standard for energy management systems.
Where the relevant energy consumption is fully covered by qualifying ISO 50001 certification, some ESOS assessment requirements, including the need for a lead assessor, may not apply.
Display Energy Certificates and Green Deal Assessments are no longer accepted as alternative compliance routes for Phase 4.
Confirming the appropriate route early helps determine what additional assessment work is required.
Where an ESOS lead assessor is required, the individual must belong to an approved professional body register.
The lead assessor reviews the assessment and confirms whether it meets the scheme's requirements.
Businesses should appoint an appropriately qualified assessor early enough to allow time for data collection, audit work and review.
A lead assessor is not required in every circumstance, including certain qualifying ISO 50001 compliance arrangements.
Organisations should establish which requirements apply to their chosen route rather than assuming an assessor is always necessary.
Where ESOS energy audits are required, businesses should prepare the relevant energy information and arrange access to operational sites.
An ESOS-compliant energy audit must analyse energy consumption and efficiency, identify energy-saving opportunities and include site visits.
As far as reasonably practicable, the audit must use verifiable energy consumption data covering a qualifying 12-month period.
Businesses operating multiple sites may be able to use representative site visits where the approach meets the assessment requirements.
Preparing site records, identifying relevant employees and arranging access in advance can make the audit process more efficient.
An ESOS assessment should provide more than a record of energy consumption.
Energy audits are intended to identify opportunities to reduce energy use and improve operational efficiency.
Recommendations may relate to buildings, equipment, industrial processes, transport or energy management practices.
Businesses should consider the potential savings, costs and practical requirements associated with each recommendation.
This information can support wider investment decisions and help organisations prioritise improvements that offer meaningful operational and environmental benefits.
Phase 4 introduces several important requirements that businesses should consider when preparing their assessments.
These include:
Businesses should not assume that completing the same process used during an earlier ESOS phase will automatically satisfy the Phase 4 requirements.
Reviewing current guidance is particularly important for organisations with existing energy management systems or previous ESOS assessments.
Maintaining an organised evidence pack is an important part of ESOS compliance.
Businesses should retain records supporting their assessment, including relevant energy consumption data, calculations, audit information and details of the compliance route used.
The evidence pack should also contain the records required to demonstrate that the assessment meets ESOS requirements.
Having information organised throughout the process can make it easier to respond to questions, review calculations and prepare the final compliance notification.
ESOS requires management involvement before the final compliance notification is submitted.
For Phase 4, the ESOS assessment and the content of the notification of compliance must be signed off by a board-level director or an appropriate person exercising management control within the participant group.
This is separate from any review and sign-off required from an ESOS lead assessor.
Businesses should establish who will provide management approval early in the process.
Leaving sign-off arrangements until the deadline approaches can create avoidable delays, particularly in organisations with several entities or management layers.
Qualifying organisations must submit their notification of compliance through the government's Manage Your Energy Savings Opportunity Scheme Reporting service, known as MESOS.
The notification includes information about the organisation, its energy consumption, the compliance route used and relevant energy-saving opportunities.
Businesses must also meet the applicable Phase 4 reporting requirements concerning energy savings and previous action plan commitments.
The compliance notification must be submitted by 5 December 2027.
Preparing the information in advance gives businesses time to complete internal checks and obtain the necessary approval before submission.
Several avoidable issues can make the assessment process more difficult.
These include:
A structured preparation process can reduce these risks and help businesses complete their assessments more efficiently.
Green Economy's sustainability consultancy includes accreditation readiness support for ESOS, alongside resource and energy efficiency reviews and carbon reduction strategy development.
Its wider decarbonisation support helps businesses understand their environmental impact and identify practical opportunities to reduce energy consumption and emissions.
Businesses can also explore Green Economy's guide to ESOS vs SECR to understand how the two requirements differ, while its carbon footprinting services support the measurement and validation of business emissions.
If your organisation is preparing for ESOS Phase 4, contact Green Economy to discuss its sustainability consultancy services and the support available for your business.
We are a social enterprise building a more sustainable economy, powered by local suppliers. We help organisations leverage sustainability to grow, while helping green tech and environmental services business win new business in their local area.
If you're interested in exploring how we can help your business grow, get in touch and one of our expert advisors will be happy to help.
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