ESOS Phase 4: deadlines, who qualifies and where lighting fits

Published 2023-05-20, updated 2026-10-26

Updated 23 October 2026. This article replaces our earlier guide to ESOS Phase 2, which has now closed.

The Energy Savings Opportunity Scheme (ESOS) is a mandatory energy assessment scheme for large organisations in the UK. Organisations that qualify must carry out an assessment every four years, covering the energy used by their buildings, industrial processes and transport. The current compliance period is Phase 4.

Key dates for ESOS Phase 4

• Qualification date: 31 December 2026. Your organisation qualifies for Phase 4 if it meets the ESOS definition of a large undertaking on this date.
• Compliance deadline: 5 December 2027. This is the deadline for submitting your notification of compliance through the Manage your ESOS reporting system (MESOS).
• Phase 3 progress update: 5 December 2026. If you qualified for Phase 3, an annual progress update on your action plan is due by this date, signed off by a board level director.
• Audit data period. An ESOS energy audit must be based on 12 months of verifiable energy data, beginning no earlier than 6 December 2022 for Phase 4.

Who qualifies?

For Phase 4, a large undertaking is any UK company that either:

• employs 250 or more people, or
• has an annual turnover above £44 million and an annual balance sheet total above £38 million.

Corporate groups qualify if at least one UK group member is a large undertaking. Public sector bodies do not usually need to comply.

What has changed in Phase 4?

• Display Energy Certificates (DECs) and Green Deal assessments can no longer be used as alternative routes to compliance. You comply with an energy audit, ISO 50001 certification, or a mix of the two.
• Your assessment must report progress against your action plan commitments, and explain any commitments that were not met.
• You can voluntarily add a net zero assessment using PAS 51215-1:2025 and PAS 51215-2:2025.

The steps to compliance

1. Calculate your total energy consumption.
2. Identify areas of significant energy consumption, covering at least 95% of the total.
3. Calculate energy intensity ratios for buildings, transport, industrial processes and other uses.
4. Choose your route to compliance and appoint an ESOS lead assessor from an approved register.
5. Carry out the energy audits, including site visits.
6. Complete the ESOS report and share it with your corporate group.
7. Get board level sign off and submit the notification in MESOS by 5 December 2027.
8. Keep an evidence pack.

Penalties

The regulator can issue civil sanctions. Failing to carry out an ESOS assessment can lead to an initial penalty of up to £50,000, plus up to £500 for each working day the breach continues (up to 80 working days), and publication of the breach. The Environment Agency's enforcement and sanctions policy sets out its approach.

Where lighting fits in an ESOS audit

In warehouses, factories and distribution centres, lighting is often one of the easier energy saving opportunities to act on: it can be measured, the replacement is well understood, and controls such as presence and daylight sensors add further savings. If your ESOS audit or action plan includes a lighting upgrade, we can survey the site, design to the light levels in BS EN 12464-1 and supply and install the fittings. Every Polaris product carries a 5-year warranty.

Try our LED savings calculator for a first estimate, or request a free lighting survey and lighting design plan.

Polaris Light is not an ESOS lead assessor. Your lead assessor signs off the assessment.

Sources

• GOV.UK: Energy savings opportunity scheme (ESOS): find out if you qualify and how to comply (DESNZ and Environment Agency, last updated 2 September 2026)
• GOV.UK: Complying with ESOS phase 4
• Environment Agency: Enforcement and sanctions policy