ESOS Phase 4 Changes

What has changed

Display Energy Certificates (DECs) and Green Deal Assessments (GDAs) are no longer valid compliance routes for ESOS. From Phase 4 onwards, participants must use energy audits, ISO 50001 certification, or a combination of the two.

Why it matters

If your Phase 3 compliance relied on DECs or GDAs (for example, in public sector estates, or where GDAs were used for a portion of consumption), you will need to shift to energy audits or ISO 50001 coverage for Phase 4. This may require earlier scoping than previously planned.

What to do

Review your Phase 3 compliance route and identify any DEC or GDA coverage. Plan energy audits or ISO 50001 scope extension to cover the same consumption before 5 December 2027.

What has changed

Participants whose ISO 50001 certification covers either total energy consumption (TEC) or significant energy consumption (SEC) are now exempt from two Phase 4 requirements:

• Appointing a lead assessor
• Completing an ESOS report

In Phase 3, this exemption was narrower — it only applied where ISO 50001 covered the full TEC.

Why it matters

This is genuinely good news for organisations already investing in ISO 50001. If your certification scope covers your significant energy consumption (typically the areas of highest energy use), you can now use it as your primary compliance route without additional lead-assessor cost.

What to do

Check the scope of your ISO 50001 certification. If it covers SEC or TEC, you may qualify for the expanded exemption. If you have been considering ISO 50001 but not implemented it, the improved exemption changes the return on investment calculation.

What has changed

For the first time, participants are required to report progress against the action plan they submitted in Phase 3. The ESOS report and notification of compliance (NOC) must now include:

• A description of each measure implemented to achieve the energy savings
• The energy savings achieved by each measure
• The energy saving category of each measure (behaviour change, training, capital investment, and so on)

This information will not be published, but it must be submitted.

Why it matters

This is the most significant shift in ESOS philosophy since the scheme began. Phase 4 is the first cycle where you must demonstrate what your business actually did with the recommendations from the previous cycle. It changes ESOS from a compliance report into a real evidence base for delivery.

What to do

Locate your Phase 3 action plan. Identify which measures were implemented, calculate or estimate the energy savings achieved, and categorise each one. Start this now rather than closer to the deadline. Data may need to come from operations, finance and facilities teams, and reconstruction will be harder the further you are from the events.

What has changed

If your organisation was eligible for Phase 3 and prepared an action plan, you are now required to review that action plan as part of the Phase 4 assessment. The ESOS report and NOC must include:

• Any measures proposed in the action plan that were not implemented
• The reasons why the measures were not implemented

Again, this information will not be published, but it must be submitted.

Why it matters

This closes the loop on the Phase 3 planning exercise. It also gives your board and finance team a formal reason to revisit measures that were paused or deprioritised. In many cases, the reasons a measure was not implemented (budget cycle, personnel change, competing priority) no longer apply.

What to do

Review your Phase 3 action plan honestly. For each unimplemented measure, document the reason. Where reasons no longer apply, consider reinstating the measure into your Phase 4 plan.

Lead assessor notification

Lead assessors are now required to notify their professional body of each ESOS assessment they complete or review, along with the participant's contact details. This allows the professional body to seek consent for quality-check reviews of the ESOS report.

Notification of compliance changes

The NOC must now include additional information that was voluntary in Phase 3:

• Total number of sites covered by energy audits
• ISO 50001 certification details
• UK SIC codes only (replacing international codes used in Phase 3)

Improved recording of methods and data

Chapters 11 and appendices A1 and A2 of the ESOS guidance have been updated to improve how methods and data used for calculations are recorded. This is a data-quality change that supports better analysis and easier audit review.

MESOS user management

Alongside the regulatory changes, the Environment Agency has reminded participants to keep contacts within the MESOS reporting system up to date. This is a housekeeping recommendation rather than a regulatory change, but it matters for security and continuity.

Adding a new user:

• Select "Users and Accounts" in MESOS.
• Select the user type (Advanced or Restricted) from the dropdown, following the on-screen guidance on the two levels.
• Add the first name, last name and email of the individual.
• The user will receive an email to confirm identity and create login credentials.
• Once confirmed, change the status from Accepted to Active to enable sign-in.

Disabling or removing a user:

• Select "Users and Accounts".
• To disable, change the status to Disabled on the user line.
• To remove completely, select Remove on the user line.