Energy Savings Opportunity Scheme

ESOS is the UK's mandatory energy audit scheme for large undertakings, run on a four-year cycle. It implements the energy audit requirement of the EU Energy Efficiency Directive (retained in UK law post-Brexit) and is administered by the Environment Agency.

An organisation is in scope if it meets either threshold in the qualification period:

• 250 or more employees in the UK; or
• Annual turnover above £44m and balance sheet above £38m (Phase 4 figures).

Qualifying organisations must:

• Audit at least 95% of significant energy consumption across buildings, transport and industrial processes.
• Have the audit signed off by an approved Lead Assessor.
• Notify the Environment Agency of compliance by the phase deadline.

The Phase 4 compliance deadline is 5 December 2027. Phase 4 introduces additional reporting expectations including a public-facing ESOS action plan — a step closer to the energy management standard ISO 50001 in spirit.

Procurement decisions taken between phases should be aligned to the ESOS recommendations rather than treated as a separate workstream — otherwise the audit produces recommendations that are then overwritten by the next contract before they can be implemented.