ESOS phase 4 and business travel: who qualifies, and which travel counts

The Energy Savings Opportunity Scheme makes large UK organisations audit their energy use every four years. Phase 4 has a qualification date of 31 December 2026 and a deadline of 5 December 2027, and the Environment Agency published its phase 4 guidance in July 2026. Transport is one of the four areas an ESOS assessment must cover, and the line it draws through business travel is the same one SECR draws: cars on business use are in, including employees’ own cars on mileage claims; flights, trains and taxis are out. This page quotes the GOV.UK and Environment Agency guidance on who qualifies, what is due when, and how to measure the travel part.

What ESOS is

The assessment must cover at least 95% of energy use: areas of significant energy consumption “must account for at least 95% of your total energy consumption.” It is signed off by an ESOS lead assessor unless an exemption applies, approved by a board-level director, and notified through the Environment Agency’s MESOS system.

Who qualifies for phase 4

“Your organisation qualifies for ESOS phase 4 if, on 31 December 2026, it meets the ESOS definition of a large undertaking.” A large undertaking meets either or both of these: “It employs 250 or more people.” or “It has an annual turnover in excess of £44 million and an annual balance sheet total in excess of £38 million.” Corporate groups qualify if any UK group member is large, and the whole group then takes part. “Public sector organisations do not usually need to comply with ESOS.”

Size is sticky: an undertaking “it retains that status until it falls within the definition of a small or medium undertaking (or a large undertaking, as the case may be) for 2 consecutive accounting periods.” A company that has just grown past the thresholds may not yet be in scope; one that has just shrunk may still be.

ESOS and SECR use different tests

The employee test is the same number but works differently: for ESOS, 250 employees alone is enough; for SECR, a company with 250 or fewer employees is still in scope unless it is also under one of the financial limits. The guidance itself points out the overlap: “ESOS is separate to the Streamlined Energy and Carbon Reporting (SECR) framework”, but systems that collect energy data for one can serve the other. SECR in detail is on SECR and business travel.

The dates

• 5 December 2026: phase 3 participants — “an annual progress update is due to be submitted by 5 December 2026 in relation to the action plan you submitted.”
• 31 December 2026: phase 4 qualification date.
• 5 December 2027: “The deadline for submitting a notification of compliance for phase 4 of ESOS is 5 December 2027.”
• 5 December 2028: “complete an ESOS action plan by the action plan deadline of 5 December 2028”, with annual progress updates after that.

Phase 4 also changes the routes to compliance: “you can no longer use Display Energy Certificates (DECs) and Green Deal assessments (GDAs) as alternative compliance routes”

Business travel in ESOS

“Energy consumption from transport is included in ESOS.” The test, as in SECR, is who buys the fuel:

The guidance lists what to include — among them “personal or hire cars on business use” — and what to leave out: “train travel of your employees where you do not operate the train”, “flights your employees take where you do not operate the aircraft” and “taxi journeys your employees take where you do not operate the taxi firm”. For aircraft an organisation does operate, “A participant’s energy consumption includes energy consumed for the purposes of transport by an aircraft or a vessel during any journey which starts, ends, or both starts and ends within the UK.”

Measuring it from mileage claims

Mileage claims are the obvious data for employees’ own cars, with a caveat: “You could use data from employee mileage claims to gather mileage data. However, this would not be counted as verifiable data unless the method of reporting includes submissions from odometer readings, so should be treated as an estimate.” Estimates are allowed — “For instance, you could use the number of expensed miles multiplied by an average fuel consumption factor to estimate the usage” — provided they are notified and the method is kept in the evidence pack. Appendix C works an example and states: “Expensed mileage can be converted into energy use by applying standard conversion factors, such as those included in the UK government conversion factors for company reporting.” The 2026 car factors are on business travel emissions factors.

Transport also needs its own energy intensity ratio. The recommended indicator for passenger transport is “Person mile travelled (for passenger transport) or tonne mile travelled (for freight transport)” — for business mileage, miles multiplied by the number of people in the car.

Where travel savings come from

An ESOS audit has to identify energy saving opportunities in transport as well as buildings. With flights, rail and taxis excluded, an office-based organisation’s transport energy in scope is likely to be mostly cars on business, so the opportunities sit in the travel policy: which journeys are driven, in what, and whether rail — outside ESOS because the organisation does not operate the train — or a pool car is the default. The grey fleet page covers the same journeys from the health and safety side.

A checklist for the travel side of ESOS

• Check qualification on 31 December 2026 for every UK group member, using the two-year rule.
• Pull business mileage for company, personal and hire cars; flag which figures come from odometer readings.
• Record fuel bought for hire cars, and any company-operated aircraft or vessels.
• Calculate a transport energy intensity ratio in person miles.
• Give the lead assessor the travel policy, so savings opportunities can be framed as policy changes.
• If also in SECR scope, use the same mileage data for both.

This page quotes GOV.UK and Environment Agency guidance as read on 2026-10-04; it is not a substitute for the full phase 4 guidance or a lead assessor’s advice.

Common questions