ESOS Phase 4

Made Easy

With 51toCarbonZero

The Energy Savings Opportunity Scheme (ESOS) is the UK’s mandatory energy assessment scheme for large organisations, run in four-year phases by the Environment Agency. Phase 4 is now under way: the qualification date is 31 December 2026, and compliance must be notified through the government’s MESOS portal by 5 December 2027.

If your organisation took part in Phase 3, it will most likely qualify again. If you didn’t qualify last time but have grown since, through hiring, rising turnover or acquisition, this may be the first phase that brings you into scope. Either way, the work takes months rather than weeks: data gathering across every site and vehicle, audits, and a report signed off at board level. The time to start is now.

The Phase 4 timeline

Who has to comply

You must take part if, on 31 December 2026, your organisation or any UK undertaking in its corporate group is a ‘large undertaking’, meaning either:

250 or more employees (the average monthly headcount, every person counting as one regardless of hours), or
an annual turnover above £44 million and a balance sheet total above £38 million.

The tests run company by company across the whole UK group, so one qualifying company brings the entire group in, and the highest UK parent normally notifies. Status is sticky: it changes only after two consecutive years on the other side of the thresholds. Public bodies are excluded, and lighter routes apply to ISO 50001 holders and very low energy users (below). Non-compliance risks civil penalties of up to £50,000 with daily additions, and the regulators publish the names of organisations that miss their obligations.

What compliance involves

Measure your total energy for a 12-month reference period that includes 31 December 2026, in kWh, across buildings, transport and industrial processes.
Identify your significant consumption: audits must cover at least 95% of the total.
Appoint a lead assessor and audit the sites, fleet and processes involved, ideally to the EN 16247 standards. Estates can be sampled.
Compile the ESOS report, covering the savings opportunities found with costs and paybacks, and, new for Phase 4, a review of your Phase 3 action plan and the savings achieved since.
Have a director sign off, then notify through MESOS by 5 December 2027, keeping an evidence pack behind the numbers.
Submit an action plan by 5 December 2028, followed by three annual progress updates.

Two lighter routes exist: ISO 50001 certification covering your total or significant consumption removes the need for a separate ESOS audit, and organisations using under 40,000 kWh a year make a simpler low-energy notification.

What’s changed since Phase 3

Phase 4 tightens the paperwork rather than the method:

Display Energy Certificates and Green Deal Assessments no longer count as compliance routes.
Every figure must be in kWh, transport fuel included.
The notification needs UK SIC codes, the number of audited sites and any ISO 50001 certificate details.
You must report the measures implemented since Phase 3 and the energy each one saved.
Any Phase 3 action-plan commitments not delivered must be identified and explained.

None of this is difficult where the records exist, but gathering four years of implementation evidence is slow, which is another argument for starting early.

How we help

51toCarbonZero runs ESOS end to end, with a named specialist and our in-house ESOS lead assessor alongside you throughout.

We confirm whether and how you qualify, capturing the MESOS company information in the same conversation. For existing clients most of this is already on file.
Data collection. Bills, meter readings and fleet records, in whatever state they’re in, collated into a complete 12-month energy picture in kWh. For SECR clients, data is collected once and reused for both schemes.
Our lead assessor plans and carries out the site and fleet assessments to EN 16247, agreeing the approach before anyone is on site.
Costed measures with annual kWh, cost and carbon savings, capital cost and payback, ranked against the criteria that matter to you.
Report and submission. We write the report, including the Phase 3 action plan review, steer director sign-off and submit through MESOS on your behalf.
Action plan and updates. We draft the 2028 action plan, handle the three progress updates and help you implement the measures, which is where the value sits: 80% of listed companies have a net zero ambition, yet only 11% have achieved any actual carbon reduction.

Clients who completed Phase 3 with us start ahead: the baseline, site list, previous recommendations and MESOS access are already in our system.

Where to start

A short call with your headcount, turnover and balance sheet figures to hand usually settles whether Phase 4 applies. From there we can map your sites, agree the audit plan and set a timetable that lands comfortably ahead of December 2027, avoiding the rush that builds before an ESOS deadline.

Get in touch at info@51tocarbonzero.com or on 020 4578 4040, or speak to your Climate Success Manager if you’re already working with us.

Emma Littlewood
ESOS Lead Assessor Elmhurst CJ32-0001: Buildings, Transport, Processes.