ESOS Phase 4: what to do now

The Energy Savings Opportunity Scheme (ESOS) is now in Phase 4. Jon Cranefield, Head of Responsible Consumption at Sustainable Energy First, explains what businesses should be doing at this point.

The ESOS Phase 4 deadline is 5 December 2027, which feels like a long way off. But there are actions you can take now that will make Phase 4 compliance more straightforward in the long run.

Look for a lead assessor

It’s not too early to appoint a lead assessor for Phase 4, especially if you’ll be requiring them to carry out the energy audits themselves. Even if their role is limited to checking the work of your in-house team, it’s still a smart idea to get them booked in now.  Don’t leave it until the ESOS Phase 4 deadline is approaching or you risk not getting it signed off in time.

Sustainable Energy First has a qualified team who can handle the ESOS lead assessor role for your organisation.

Keep gathering data

Data collection should be ongoing, rather than something you do in bursts ahead of compliance deadlines. The more detail the better, so use sub-metering data to break down energy consumption by sites and processes.

As well as energy use, you should also be measuring energy intensity ratios. These are now a staple of both SECR and ESOS reporting. They’re important because they put energy use in the context of other metrics like productivity, floorspace or footfall. If your energy consumption rises 10% in a year, that could look like a step backwards – but if this happens in line with a 20% rise in output, it’s clear that your business is successfully implementing efficiency measures.

Build on Phase 3 to create your Phase 4 plan

Phase 3 introduced two new ESOS compliance requirements:

• An Action Plan
• Two subsequent progress reports

If your business was in scope for Phase 3, you will have already (as of March 2026) completed the plan and the first progress report. You’ll need to submit the second progress report by 5 December 2026. (The guidance suggests that you don’t do it too far ahead of this deadline.)

This stage is a great opportunity for honest internal discussions and tough questions.

• If we didn’t achieve everything in the Action Plan, what didn’t get done?
• What were the barriers to carrying out all the measures in the Action Plan?
• If we achieved it all, how could the next plan be more ambitious?
• How much money has the business saved through energy-saving measures?
• What were the big wins?
• Where did we really mess up?

Not everything has to go into your official progress reports, but this is material you can draw on when you’re creating your Action Plan for ESOS Phase 4.

When to start on ESOS Phase 4

The first step is the energy audit, whether you do that in-house or hire a lead assessor. This must be based on 12 months’ energy data. The 12-month reference period for your total energy consumption has to:

• Include the qualification date (31 December 2026)
• End before the final ESOS Phase 4 deadline (5 December 2027)

So the earliest it could have started is 1 January 2026, and the latest it could end is 4 December 2027. (The rules are slightly different for significant energy consumption, as opposed to total consumption, but we would always advise using the same reference period for both.)

The bigger your organisation is, the more resources and time the energy audit will take, especially if you’re doing the bulk of the work in-house. Even if you hire a lead assessor for the audit, you still need to work with them to provide the information they need. So it makes sense to start on your Phase 4 energy audit as soon as possible.

What is the qualification date?

The qualification date for ESOS Phase 4 is 31 December 2026. Your business is in scope if, on that date:

• It employs 250 or more people;
• and has an annual turnover in excess of £44 million
• and has an annual balance sheet total in excess of £38 million.

In practice, the vast majority of organisations in scope of Phase 3 will also be in scope of Phase 4. Unless your organisation has been through huge changes, there is no need to wait until the qualification date to start preparing for your ESOS Phase 4 compliance.

Key dates

Getting expert help

At Sustainable Energy First, we have been supporting large organisations with their ESOS obligations since the scheme began over a decade ago. We’re now beginning to take queries about ESOS Phase 4 compliance, and we expect many more calls in the coming months. We can take on the lead assessor role for you, or just advise your organisation on its methodology. For a no-obligation chat, get in touch today.