Energy Savings Opportunity Scheme (ESOS)
ESOS Phase 4 is a four-year snapshot. Keep the action plan measurable between cycles.
ESOS Phase 4 of the Energy Savings Opportunity Scheme is a mandatory energy assessment for large UK undertakings. You qualify on 31 December 2026 and notify compliance by 5 December 2027 via MESOS. The assessment covers buildings, industrial processes and transport every four years. Between cycles, action-plan progress and savings evidence still need a continuous read. FrostLogic Explore keeps that evidence measurable without replacing your lead assessor or MESOS filing.
Statutory duty
What ESOS Phase 4 requires
ESOS applies to large UK undertakings and their corporate groups. Qualification is tested on 31 December 2026. The notification of compliance deadline for Phase 4 is 5 December 2027, submitted through MESOS. Groups qualify if at least one UK member meets the large-undertaking test. UK establishments of overseas companies may also be in scope when the UK group qualifies.
Public-sector bodies usually sit outside ESOS. If you previously qualified but do not meet the Phase 4 threshold, tell your regulator. Full rules live on gov.uk ESOS guidance. For the continuous layer between assessments, see energy management software and the compliance hub.
Action plans and progress reporting
Phase 4 tightens the link between the assessment and what you said you would do next. Your ESOS assessment must include progress against action-plan commitments and explain commitments that were not met. It also needs more detail on energy savings achieved since the previous compliance date. That is the product bridge: a four-year snapshot still needs week-by-week evidence that measures held. Explore reads the same meters and sensors so drift shows up before the next ESOS Phase 4 assessment, not only in the MESOS pack. See also energy efficiency in commercial buildings and energy monitoring and targeting.
Routes to compliance
You comply with an ESOS energy audit or with ISO 50001 certification covering significant energy consumption or total energy consumption. From Phase 4, Display Energy Certificates (DECs) and Green Deal assessments (GDAs) are no longer compliance routes. An ISO 50001 certificate used for this route must be issued after 5 December 2023 and remain valid on 5 December 2027. Lead-assessor sign-off is not required when significant or total energy consumption is covered by ISO 50001, or when total energy consumption is below 40,000 kWh. An energy management system can support that route; Explore is the continuous read around it, not a substitute for certification or the lead assessor.
SECR reporting and ESOS: related, not the same duty
Streamlined Energy and Carbon Reporting (SECR) is a Companies Act carbon-and-energy disclosure for qualifying UK companies. ESOS is a separate energy-assessment scheme under the Energy Savings Opportunity Scheme Regulations. Overlap in the data you collect is common; the filing routes and the statutory questions are not. This page covers ESOS Phase 4 and ESOS compliance. It does not replace SECR reporting guidance.
Between cycles
What Explore does with your ESOS findings between assessments
Deviation detection
Several detection methods score each meter and sensor deviation against the building's own history, so an operating change that undoes a savings measure shows up promptly, not only at the next ESOS Phase 4 checklist review.
Forecasting
Forecasts with clear confidence bands show whether consumption is drifting from the assumptions in your last assessment, early enough to correct course.
Continuous evidence
The same engine that holds BREEAM, LEED and Nordic Swan evidence also keeps a timestamped trail against action-plan items, so progress reporting has meter-backed numbers between MESOS filings.
Before you ask
ESOS Phase 4 FAQ
Large UK undertakings and their corporate groups. On 31 December 2026 a large undertaking employs 250 or more people, or has annual turnover above £44 million and an annual balance sheet total above £38 million. Groups qualify if at least one UK member meets the test. UK establishments of overseas companies may be in scope when the UK group qualifies.
Qualification is tested on 31 December 2026. The deadline for submitting a notification of compliance for Phase 4 is 5 December 2027 via MESOS. Assessments run every four years.
DECs and Green Deal assessments are no longer compliance routes. Assessments must include progress against action-plan commitments and explain unmet ones. Reports need more detail on energy savings achieved since the previous compliance date. The ISO 50001 route now covers significant energy consumption as well as total energy consumption.
Yes, when ISO 50001 covers significant or total energy consumption. The certificate must be issued after 5 December 2023 and valid on 5 December 2027. Lead-assessor sign-off is not required when significant or total energy consumption is covered by ISO 50001, or when total energy consumption is below 40,000 kWh. Otherwise you need an ESOS lead assessor for the assessment.
No. From Phase 4 onwards, Display Energy Certificates (DECs) and Green Deal assessments (GDAs) can no longer be used as alternative compliance routes. You comply via an ESOS energy audit or qualifying ISO 50001 certification.
SECR (Streamlined Energy and Carbon Reporting) is a carbon and energy disclosure under company law. ESOS is a separate mandatory energy-assessment scheme. They can share source data, but they are different duties with different filing routes. This page addresses ESOS, not SECR reporting software.
If you qualified for ESOS Phase 3, an annual progress update on the action plan is due by 5 December 2026 via MESOS, with board-level sign-off. That Phase 3 reminder is separate from the Phase 4 qualification date (31 December 2026) and the Phase 4 notification deadline (5 December 2027).
No. Explore does not replace an ESOS lead assessor, MESOS filing, or UK regulators such as the Environment Agency. Continuous monitoring fills the gap between assessments and supports action-plan evidence. The statutory assessment and notification remain yours.
Bring the findings from your last ESOS assessment.
We will show how Explore keeps action-plan progress and savings evidence measurable between cycles, using a slice of your own data.