ESOS Phase 4 explained: deadlines, requirements and how to prepare

For organisations that fall within scope, ESOS Phase 4 brings updated reporting requirements and a greater emphasis on demonstrating progress against energy-saving commitments.

Although the compliance deadline is still over a year away, preparing early can help organisations avoid last-minute challenges, manage the assessment process more effectively and identify opportunities to reduce energy consumption and costs.

In this guide, we explain what ESOS Phase 4 involves, who needs to comply, the key deadlines and what your organisation can do now to prepare.

What is ESOS Phase 4?

The Energy Savings Opportunity Scheme (ESOS) is a mandatory energy assessment scheme for large UK organisations, introduced to encourage businesses to identify opportunities to improve energy efficiency.

Every four years, qualifying organisations must assess their energy consumption across buildings, industrial processes and transport, and identify cost-effective Energy conservation measures (ECMs) to reduce energy use.

ESOS Phase 4 is the fourth compliance period of the scheme, running from 6 December 2023 to 5 December 2027.

While ESOS does not generally require organisations to implement every energy-saving recommendation identified, it does require qualifying organisations to complete the necessary assessments, report their findings and meet ongoing reporting obligations.

ESOS is more than a compliance exercise. When approached strategically, it can provide valuable insight into energy performance, highlight inefficiencies and support investment decisions that deliver long-term operational and financial benefits.

Who needs to comply with ESOS Phase 4?

ESOS applies to large UK undertakings and qualifying corporate groups.

Your organisation will generally need to comply with ESOS Phase 4 if, on 31 December 2026, it meets either of the following criteria:

• Employs 250 or more people.
• Has an annual turnover exceeding £44 million and an annual balance sheet total exceeding £38 million.

Corporate groups may also qualify if at least one UK group member meets the criteria. Specific rules apply to corporate structures and UK establishments of overseas companies.

Organisations that qualified for previous phases should not automatically assume their position remains unchanged. Changes in employee numbers, financial performance, acquisitions or group structures for two consecutive accounting periods could affect eligibility.

If your organisation is approaching the qualification thresholds, reviewing your position ahead of 31 December 2026 will help establish whether ESOS Phase 4 applies.

What are the ESOS Phase 4 deadlines?

There are several important dates organisations should be aware of when planning for ESOS Phase 4.

The key deadline for ESOS Phase 4 compliance is 5 December 2027. By this date, qualifying organisations must have completed their assessment and submitted their notification of compliance.

However, organisations should also be mindful of their outstanding Phase 3 obligations, particularly the second Action Plan progress update due on 5 December 2026.

Starting preparations early can help ensure sufficient time to collect and validate energy data, arrange site audits, appoint a Lead Assessor and complete the necessary reporting. 

What has changed for ESOS Phase 4?

ESOS Phase 4 builds on the requirements introduced during Phase 3, with further changes designed to strengthen accountability and encourage organisations to act on identified energy-saving opportunities.

The latest amendments to the scheme, introduced in 2026, include several important changes.

1. Greater accountability for energy-saving commitments

Under Phase 4, organisations must provide additional information about the energy conservation measures implemented during the compliance period.

This includes reporting the measures undertaken, the energy savings achieved and the relevant energy-saving categories.

Organisations must also review their previous Action Plan commitments, identify measures that have not been implemented and explain why.

These changes place greater emphasis on tracking and demonstrating progress, rather than simply identifying opportunities through an assessment.

2. Changes to alternative compliance routes

Display Energy Certificates (DECs) and Green Deal Assessments (GDAs) can no longer be used as alternative routes to ESOS compliance.

Qualifying organisations will generally need to undertake ESOS-compliant energy audits, use qualifying ISO 50001 certification, or use an appropriate combination of these routes.

3. Updated requirements for ISO 50001-certified organisations

Organisations using ISO 50001 certification as their compliance route may benefit from reduced administrative requirements.

Where qualifying certification covers the organisation's significant or total energy consumption, an ESOS report and Lead Assessor may not be required.

However, the certification must meet the relevant Phase 4 requirements, and organisations must still fulfil applicable notification and reporting obligations.

4. An additional Action Plan progress update

ESOS Phase 4 introduces a third progress update for the Action Plan, due by 5 December 2031.

This extends the reporting period and reinforces the importance of maintaining reliable records of energy-saving measures and their outcomes.

For organisations, these changes mean that good data management, accurate reporting and ongoing monitoring of energy performance are increasingly important parts of ESOS compliance.

What does an ESOS Phase 4 assessment involve?

Qualifying organisations must complete a structured assessment of their energy consumption and identify opportunities to improve energy efficiency.

The main steps include:

1. Calculate total energy consumption

Establish how much energy your organisation consumes across its buildings, industrial processes, transport and other relevant activities.

2. Identify significant energy consumption

Determine which activities and assets account for at least 95% of your total energy consumption. These must be covered by an appropriate compliance route.

3. Calculate energy intensity ratios

Assess energy consumption against relevant measures of activity, such as production output, floor area or distance travelled, to provide greater context around energy performance.

4. Complete the required energy audits

Undertake compliant energy audits to assess how energy is being used and identify key energy conservation measures that will provide opportunities to improve efficiency.

For organisations operating across multiple sites, a representative sampling approach should be adopted where appropriate. This involves selecting sites or activities that reflect the organisation's wider energy consumption, operational characteristics and energy-saving opportunities.

The sampling methodology must be justified and documented to demonstrate that the audits provide appropriate coverage of significant energy consumption.

5. Appoint an ESOS Lead Assessor where required

A qualified Lead Assessor reviews the assessment and helps ensure it meets the scheme's requirements. Specific exemptions apply to certain ISO 50001 compliance routes and other qualifying circumstances.

6. Prepare the ESOS report and supporting evidence

Document the assessment, energy-saving opportunities, relevant progress against previous commitments and the information required to demonstrate compliance.

7. Obtain director sign-off and submit the notification

Complete the necessary approval process and submit the notification of compliance through the government's Manage your Energy Savings Opportunity Scheme Reporting (MESOS) system.

For organisations with multiple sites, complex energy systems or large volumes of consumption data, the process can require considerable coordination.

Having the right systems, expertise and support in place can make compliance more manageable.

For organisations operating across multiple sites, a representative sampling approach may be adopted where appropriate. This involves selecting sites or activities that reflect the organisation's wider energy consumption, operational characteristics and energy-saving opportunities.

The sampling methodology must be justified and documented to demonstrate that the audits provide appropriate coverage of significant energy consumption.

How can your organisation prepare for ESOS Phase 4?

Although the compliance deadline is December 2027, there are several practical steps organisations can take now to reduce the pressure of meeting the requirements.

Review your previous ESOS assessment and Action Plan

Start by reviewing your Phase 3 assessment, the energy-saving opportunities identified and the commitments included in your Action Plan.

Consider which recommendations have been implemented, what savings have been achieved and whether there are any outstanding actions.

This will help identify potential gaps in your reporting and establish a clearer starting point for Phase 4.

Get your energy data in order

One of the biggest challenges organisations face during ESOS assessments is collecting accurate and complete energy consumption data.

Review how energy data is currently collected, stored and managed across your organisation.

This should include energy used by buildings, industrial processes and transport, as well as any gaps or inconsistencies in the information available.

Improving data collection now can save considerable time later in the compliance process.

Confirm your organisational scope

Review your organisational structure, including subsidiaries, acquisitions and other relevant group arrangements.

Understanding which entities and activities fall within scope will help ensure the assessment is planned appropriately.

Plan your energy audits early

If your organisation operates across multiple sites, arranging energy audits early can help avoid scheduling difficulties as the deadline approaches.

It also provides more time to evaluate the findings and consider which recommendations could deliver the greatest operational and financial benefits.

Engage an experienced ESOS Lead Assessor

Working with an experienced Lead Assessor can help your organisation navigate the requirements, identify potential compliance risks and ensure the assessment provides useful insights.

Early engagement also allows time to develop a structured approach to data collection, site assessments and reporting.

Getting more value from ESOS Phase 4

While compliance is mandatory for qualifying organisations, the findings of an ESOS assessment can offer benefits that extend well beyond meeting regulatory requirements.

A thorough assessment can help organisations:

• Identify appropriate energy conservation measures to reduce energy consumption and operating costs.
• Improve the efficiency of buildings, equipment and industrial processes.
• Prioritise energy-saving projects based on their potential financial and operational benefits.
• Strengthen energy data management and reporting.
• Support wider resource efficiency and business resilience objectives.

For example, through our work with food manufacturer Greencore, JRP Solutions identified £6.3 million in potential annual energy savings through energy audits and ESOS compliance support.

The value of ESOS lies not only in identifying opportunities, but also in helping organisations understand which improvements are worth pursuing and how to turn recommendations into practical action.

How JRP can support your ESOS Phase 4 compliance

At JRP, we help organisations navigate ESOS requirements while identifying opportunities to improve energy performance and reduce costs.

With over 600 audits completed and a 100% compliance rate, our experienced team of ESOS Lead Assessors and energy consultants provides practical support throughout the assessment and reporting process.

Our support includes:

• ESOS compliance assessments and energy audits.
• Accredited Lead Assessor services.
• Energy data collection, analysis and reporting.
• Identification and prioritisation of energy conservation measures.
• Support with Action Plans and progress reporting.
• Tools to organise compliance information and track energy-saving projects.

We also provide access to our purpose-built ESOS Organiser and Project Activator tools, helping organisations manage assessment information and monitor progress against identified opportunities.

Our approach is designed to make ESOS compliance straightforward while ensuring organisations gain meaningful value from the process.

Book a free ESOS Phase 4 Health Check

Not sure whether your organisation is ready for ESOS Phase 4?

Our free 30-minute ESOS Phase 4 Health Check gives you the opportunity to speak with an ESOS specialist about your current position, previous Action Plan commitments and preparation for the next compliance deadline.

We'll help you identify potential gaps, clarify the requirements and understand what steps you may need to take.

Book your free ESOS Phase 4 Health Check

Alternatively, find out more about our ESOS compliance service.