Energy Savings Opportunity Scheme (ESOS) – 2025 Compliance Guide
As ESOS Lead Assessors, we help organisations meet their legal obligations while identifying practical, cost-effective energy savings. Every ESOS assessment we have delivered to date has uncovered meaningful “no-cost, low-cost and fast-payback” opportunities that reduce ongoing energy spend.
What Is ESOS?
The Energy Savings Opportunity Scheme (ESOS) is a mandatory energy assessment and energy-saving identification programme for large UK organisations. It requires qualifying businesses to measure their total energy consumption and undertake audits covering buildings, industrial processes, and transport.
ESOS operates in four-year cycles. We are currently in Phase 4 (2023–2027).
Who Needs to Comply?
You must participate in ESOS if your organisation is a large undertaking on the qualification date 31 December 2026, defined as:
- 250 or more employees,
- OR annual turnover > £38.93 million and annual balance sheet total > £33.486 million,
- OR you are part of a corporate group that meets these thresholds.
These criteria remain unchanged for Phase 4.
What’s New in ESOS Phase 4?
Net Zero Requirements Delayed to Phase 5
The government has postponed mandatory net-zero elements until Phase 5 (2027–2031).
This gives organisations more time to prepare.
Several Phase 4 Changes Still Apply (pending parliamentary approval)
- Display Energy Certificates (DECs) and Green Deal Assessments (GDAs) are no longer valid compliance routes.
- Organisations must demonstrate progress against their ESOS action plan during their next assessment.
- If progress is limited, an explanation must be provided.
- Voluntary net zero reporting can now be included in Phase 4.
New PAS Net Zero Standards (from Feb 2025)
DESNZ and the British Standards Institution (BSI) have introduced two optional PAS standards for organisations wishing to integrate net zero planning into ESOS:
- PAS 51215-1:2025 – How to conduct an integrated energy and decarbonisation assessment.
- PAS 51215-2:2025 – Competency framework for assessors undertaking energy and carbon assessments.
Using PAS 51215-1:2025 allows businesses to voluntarily include:
- Greenhouse gas (GHG) emissions linked to energy use
- Net zero governance and risk assessments
- A structured net-zero implementation plan
2025 Compliance Requirement: Initial Progress Update (PU1)
All ESOS participants must submit a Progress Update (PU1) by 5 December 2025.
What you need to know
- This follows the Action Plan submission deadline of 5 March 2025.
- All participants must submit a PU1 – even if no energy-saving measures were identified or implemented.
- PU1 must be submitted through MESOS, which went live mid-June 2025.
- All data must be manually entered.
- Only the responsible undertaking can submit the update.
Disaggregated Undertakings
If your company has since left a parent group that originally submitted the Action Plan, you may now need to submit your own PU1.
This may require creating a new MESOS account.
Don’t Miss the Deadline
Failure to submit PU1 can lead to enforcement action from the regulator.
Our ESOS Services: Compliance + Real Savings
We don’t just help you comply – we help you reduce energy costs and build a pathway toward carbon reduction.
We Provide:
- Full ESOS Phase 4 assessments
- ESOS Lead Assessor sign-off
- Energy audits for buildings and processes
- Action Plan preparation and Progress Update support
- Identification of low-cost and no-cost savings
- Practical advice on implementation and payback
Every assessment we have delivered has identified actionable, financially beneficial savings.
Why Start Now?
Starting early means:
- Lower assessment and audit costs
- Less operational disruption
- More time to implement easy improvements
- Better preparation for mandatory net-zero requirements in Phase 5
- Avoiding fines, which can be up to £50,000 for non-compliance
We support organisations through the full ESOS process – from energy data collection and auditing to final submission and progress reporting.
Contact us today to start planning your Phase 4 compliance and unlock meaningful energy savings.
