ESOS Phase 4 - 2026/2027

ESOS Reference Guide

Everything you need to understand and meet your Phase 4 obligations by 5 December 2027. Written by Hawley Energy's CIBSE-accredited lead assessors.

CIBSE AccreditedESOS Certified SpecialistsPhase 4 UpdatedDeadline: 5 Dec 2027
Contents
  1. 1.Why Act Now?
  2. 2.The Hawley Energy Approach
  3. 3.How Enerlyse Makes ESOS Easier
  4. 4.What is ESOS?
  5. 5.Key Dates and Periods
  6. 6.What's Changed: Phase 4 vs Phase 3
  7. 7.Step-by-Step Compliance Process
  8. 8.Hints, Tips and Best Practice
  9. 9.Reporting and Evidence
  10. 10.Frequently Asked Questions
ESOS Phase 4 Submission Deadline
5 December 2027 - Time Remaining
520
Days
02
Hours
42
Mins
25
Secs
Don't leave compliance to the last minute. Start your audit now.

Why Start Now? The Deadline is December 2027.

It is tempting to look at a 2027 deadline and think there is plenty of time. But Phase 4 has changed the game. The organisations that act early do not just comply more easily - they save more money.

Audits done now deliver immediate savings
Every month without an audit is a month of avoidable energy spend continuing unchecked. Organisations that start now identify real savings in 2026 and bank them - rather than just filing a report at the end of 2027.
Phase 3 progress gets harder to reconstruct
Documenting what you did with Phase 3 recommendations is now mandatory. The longer you wait, the harder it becomes - people move on, records get lost, and memories fade. Start while the information is still accessible.
Lead assessors get booked up
CIBSE-accredited assessors have limited capacity. Organisations that leave it late in 2027 will compete for assessor time, pay more for it, or risk missing the deadline entirely.
Board sign-off takes longer than you think
The report requires board-level sign-off. In large organisations, getting that scheduled, reviewed, and approved can take months. Starting early builds that time in comfortably.
New audit flexibility means you can start before qualification
Phase 4 allows site audits before the 31 December 2026 qualification date. That is a genuine window to spread the workload across 2026 rather than cramming everything into a few months.
Annual progress updates start the clock post-submission
After you submit, annual updates are required with board sign-off. Starting early means your first update cycle is manageable, not rushed alongside everything else.
The Hawley Energy Approach
We turn ESOS compliance into a competitive advantage.

Most consultancies treat ESOS as a tick-box exercise. You pay for an audit, receive a report, file it with the Environment Agency, and move on. The report sits in a drawer. Nothing changes. The cost delivers no return.

We do it differently. Every audit we carry out is designed to deliver immediate commercial benefit. We identify real, implementable savings from day one - not theoretical recommendations that never leave the page.

That means the savings we find during your ESOS audit start reducing your energy costs now. By the time you submit your compliance notification in 2027, the audit has already paid for itself - and then some.

Insight before intervention
We use data and monitoring to understand your energy profile before recommending anything. No guesswork, no generic solutions.
Savings that start immediately
Our audits identify quick wins and behavioural changes that reduce costs from the first month - not just long-term capital projects.
Compliance becomes cheaper
When the savings from your audit exceed the cost of the audit itself, ESOS stops being an expense and becomes an investment with measurable return.
Fully independent advice
We are supplier and technology agnostic. No hidden commissions, no preferred products. Just honest, evidence-based recommendations.
“ESOS should not be a cost you endure. It should be the starting point for savings you would not have found otherwise.”
Hawley Energy
Enerlyse + ESOS
How Enerlyse makes ESOS significantly easier - and more valuable

One of the most time-consuming parts of any ESOS audit is data gathering and analysis. Pulling together utility bills, calculating consumption by site, identifying inefficiencies, and building energy intensity ratios takes weeks when done manually.

Clients who use Enerlyse - our energy monitoring and intelligence platform - arrive at their ESOS audit with much of that work already done. The system continuously collects, structures, and analyses consumption data across your entire estate, meaning your assessor spends less time on data and more time on insights.

“Where others give you data, Enerlyse gives you decisions. For ESOS, that means faster audits, better recommendations, and compliance that actually reduces your costs.”
Data already collected
Enerlyse continuously logs consumption data across all sites. By the time your ESOS audit begins, years of clean, structured data are ready to use - no scrambling for utility bills.
Faster audit process
The data analysis phase of an ESOS audit is typically the most time-consuming. Enerlyse does much of this work automatically, significantly reducing assessor time and your overall compliance cost.
Anomalies already flagged
Enerlyse identifies unusual consumption patterns in real time. Your audit benefits from months of pre-identified inefficiencies rather than starting from scratch.
Energy intensity ratios ready
ESOS requires energy intensity ratios (kWh per m², kWh per unit output). Enerlyse calculates and tracks these continuously - they are ready to drop straight into your report.
Progress tracking built in
Phase 4 requires annual progress updates post-submission. Enerlyse tracks implementation of recommendations automatically, making those updates straightforward rather than a research exercise.
Ongoing value beyond compliance
Unlike a one-off audit, Enerlyse keeps working after submission - monitoring savings, flagging drift, and ensuring your action plan recommendations actually deliver results.

For organisations starting their ESOS journey with Hawley Energy, we recommend setting up Enerlyse monitoring at the outset. Even a few months of live data before your audit begins makes a measurable difference to the quality and speed of the process - and the savings we can identify.

After submission, Enerlyse becomes the tool that ensures your action plan commitments are tracked, your annual progress updates are straightforward, and the savings identified during your audit are actually realised.

Find out how Enerlyse can reduce your ESOS compliance cost and turn your audit into an ongoing savings engine.
Learn About EnerlyseTalk to Our Team
Need a CIBSE-accredited Lead Assessor?

Our team of CIBSE-accredited engineers have delivered ESOS compliance for organisations across the UK. We handle everything from scoping to submission.

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Section 1

What is ESOS?

The Energy Savings Opportunity Scheme (ESOS) is a mandatory UK energy assessment scheme for large undertakings. It requires regular audits of energy use across buildings, processes, and transport - and the identification of cost-effective savings opportunities.

ESOS is not just a compliance exercise. Treated correctly, it is a commercial tool that surfaces real savings and positions your organisation ahead of tightening regulation.

Who qualifies?

UK undertakings with either:

  • 250 or more employees, or
  • Annual turnover above £44m AND annual balance sheet above £38m

Important: If any company within a UK group qualifies, the entire UK group must comply.

Section 2

Key Dates and Periods

Qualification Date
31 December 2026
Submission Deadline
5 December 2027
Compliance Phase
6 Dec 2023 - 5 Dec 2027
Evidence Period
Must include 12 months covering qualification date
Section 3

What's Changed: Phase 4 vs Phase 3

DECs and GDAs no longer accepted
Display Energy Certificates and Green Deal Assessments are no longer valid as standalone compliance routes. The Environment Agency found they did not meet ESOS best practice standards. All organisations must now use energy audits or ISO 50001 as their primary compliance route.
New requirement: Action Plan Progress Reporting
You must now document and report progress against your Phase 3 action plan recommendations. This forms part of your Phase 4 ESOS assessment. Review what you committed to in Phase 3 and track what was implemented, what was not, and why.
Tip: Start this review now - it is easier to reconstruct progress while memories are fresh.
Net Zero Assessments postponed to Phase 5
Net zero requirements are not mandatory in Phase 4. You can choose to include net zero assessments voluntarily as a separate project if desired.
Audit timing flexibility
Site energy audits can now be conducted before the qualification date of 31 December 2026. Starting audits in 2026 spreads the workload, identifies savings earlier, and avoids the end-of-year rush.
Annual progress updates required post-submission
After submitting your compliance notification, you must provide annual progress updates against your action plan commitments. Board-level sign-off is required for each update. Deadlines fall 12 months after action plan submission, then annually thereafter.
Updated Lead Assessor standards (voluntary)
New voluntary PAS standards have been published (PAS 51215-1:2025 and PAS 51215-2:2025). For Phase 4, PAS 51215:2014 remains the legal requirement. The new standards can be used voluntarily for enhanced rigour.
Section 4

Step-by-Step Compliance Process

Follow these steps to achieve full Phase 4 compliance by the 5 December 2027 deadline.

1
Confirm Qualification
Review your company or group size as of 31 December 2026. Check employee headcount, turnover, and balance sheet figures. If any group entity qualifies, the whole UK group is in scope.
2
Review Phase 3 Progress
Document what you did with your Phase 3 recommendations. This is now a formal requirement - include progress in your Phase 4 assessment. Track what was implemented, what was not, and why.
Note: Start this now while the information is accessible. Waiting until 2027 makes reconstruction significantly harder.
3
Scope Your Portfolio
Include 95% or more of your total UK energy consumption across buildings, transport, and processes. Identify all sites and energy sources that need to be covered.
4
Appoint a Lead Assessor
Your lead assessor must be on an approved register such as CIBSE or the Energy Institute. They must be directly employed and hold current accreditation (MICBSE or TIET). Our team at Hawley Energy are CIBSE-accredited and can act as your lead assessor.
5
Undertake Energy Audits
Site audits can begin in 2026 - you do not need to wait until the qualification date. Focus on cost-effective measures, not just compliance. Note: DECs and GDAs alone are no longer accepted as audit evidence.
Important: DECs and Green Deal Assessments are no longer valid standalone compliance routes. Ensure you have proper energy audits in place.
6
Calculate Energy Intensity Ratios
Relate energy use to activity - for example, kWh per square metre or kWh per unit of output. This benchmarks performance and supports the identification of savings opportunities.
7
Prepare Your ESOS Report
Summarise findings, savings opportunities, and audit evidence. Include documented progress against your Phase 3 action plan. Board-level sign-off is required before submission.
8
Submit Notification of Compliance
Submit via the MESOS system by 5 December 2027. Ensure all evidence is in order and the board sign-off is complete before submitting.
9
Plan Annual Progress Updates
Commit to annual reporting on action plan progress for two years post-submission. Budget time and resource for this - it is a formal ongoing obligation, not optional.
10
Maintain Your Evidence Pack
Keep all data, calculations, audit notes, and rationale for six years. This includes your Phase 3 action plan and progress documentation.
Section 5

Hints, Tips and Best Practice

Start early
Begin audits in 2026 for best value and less stress. The qualification date is 31 Dec 2026 - you can audit before it.
Review Phase 3
Understand what you committed to and what was achieved. This is now a formal part of Phase 4.
Avoid DECs/GDAs alone
Ensure you have proper energy audits. These certificates are no longer sufficient as standalone compliance.
Use robust data
Good metering and data management make audits easier, faster, and more accurate.
Engage stakeholders early
Early buy-in from finance, facilities, and operations teams streamlines the whole process.
Look for savings
Treat ESOS as a commercial opportunity, not just a tick-box. Real savings are available.
Plan for progress updates
Budget time and resource for annual reporting over the next two years post-submission.
Check for updates
Guidance may change. Review official Environment Agency guidance regularly.
Section 6

Reporting and Evidence Requirements

Your ESOS Report must include:
  • Scope and methodology
  • Energy audits and findings
  • Savings recommendations
  • Progress against Phase 3 action plan commitments
  • Board-level sign-off
Your Evidence Pack must contain:
  • All calculations and data sources
  • Audit records and site visit notes
  • Sign-off forms
  • Phase 3 action plan and progress documentation
  • Retained for 6 years minimum
Non-compliance penalties
Fines of up to £50,000 can be issued for non-compliance. The Environment Agency has increased enforcement activity in recent phases.
Section 7

Useful Links

Official ESOS Guidance
Visit →
List of Approved Lead Assessors
Visit →
MESOS Reporting System
Visit →
📁
Ready to submit your evidence pack?

Upload your utility bills, building information, company details, and supporting evidence securely. Our team will review your submission and be in touch within 2 working days.

✓ Utility bills (3 years)
✓ Building floor plans
✓ Company details
✓ Previous audits
✓ Energy management docs
✓ Recent improvements
Upload Evidence Pack →
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Clarity. Confidence. Control.

ESOS compliance does not have to be stressful. We have guided organisations through every phase since the scheme began. Let us do the same for you.

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Frequently Asked Questions
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