Energy Savings Opportunity Scheme
(ESOS)
Phase 4 · Mandatory for large UK organisations
Deadline: 5 December 2027
Does ESOS apply to your organisation?
ESOS is a mandatory four-year energy audit for large UK organisations who meet either of the following criteria:
250+ employees
OR
Annual turnover £44m+
and
Balance sheet £38m+
- Phase 4 is now underway
1
Qualification date:
31 December 2026
2
Compliance deadline:
5 December 2027
Phase 4 is now underway, and starting early takes the strain off your organisation.
Non-compliance risks public disclosure and civil penalties enforced by the Environment Agency.
What’s changed in phase 4?
Enhanced Reporting
Mandatory reporting of total energy consumption (kWh) and energy intensity ratios across buildings, transport and industrial processes.
DECs & GDAs Removed
Display Energy Certificates (DECs) and Green Deal Assessments (GDAs) removed as valid compliance routes.
Evidence Retention
Evidence records must be retained for two subsequent compliance periods.
Net Zero Deferred
Net zero scope deferred to Phase 5 – Phase 4 remains focused on energy efficiency.
How 51toCarbonZero supports you.
Qualification and Scoping
Rapidly confirm whether you qualify and identify your areas of significant energy consumption across buildings, transport and processes.
ESOS Audit Management
Our expert in-house energy auditors conduct compliant ESOS audits — covering 12 months of verifiable data, site visits, and energy intensity ratio calculations.
Action Plans and Reporting
We draft your board-level action plan, manage MESOS submissions, and coordinate annual progress updates so deadlines are never missed.
Carbon Strategy Integration
ESOS findings feed directly into your net zero roadmap, turning compliance into measurable carbon and cost reduction.
Our approach.
ESOS audits, reports, plans and updates are verified by our in-house Lead Assessor, who is available to support you, help overcome hurdles, and support your communication with the Environment Agency where required.
Why 51toCarbonZero?
ESOS compliance is just the start. We combine regulatory expertise with practical carbon reduction support, helping you turn your ESOS assessment into a plan for greater efficiency, lower emissions and measurable business value.
Expertise you can trust
Work with experienced ESOS Lead Assessors who understand the requirements and can guide you through every stage of compliance.
Focused on outcomes
We go beyond identifying opportunities, helping you prioritise the actions most likely to reduce energy use, emissions and cost.
End-to-end partnership
From qualification and assessment through to action planning and ongoing improvement, we stay with you beyond the compliance deadline.
- Don't leave compliance to chance.
51toCarbonZero provides a one-stop service spanning energy, carbon, environmental and ESG compliance and best practice. From ESOS and ISO 14001 and ISO 50001 management systems, through to carbon reduction, net-zero transformation and climate risk and opportunity, we help you bring everything together under one experienced team.