HMRC sets out how overseas suppliers get their emissions verified for the UK CBAM

Alongside the illustrative rates and default values it published on 16 October, HMRC released a second set of guidance that matters just as much to what the UK CBAM will cost: how overseas producers monitor their emissions, how those figures are verified, and how they reach the UK importer. It runs to four guidance pages and a 313-page technical guide, and it applies to any installation whose customers want to report actual emissions in place of HMRC's default values.

The route from installation to tax return

The UK CBAM is a tax on the importer, and the guidance keeps the producer's part voluntary. An overseas installation files nothing with HMRC. If it wants its customers to use its real figures, it monitors emissions over a calendar year, from 1 January to 31 December, appoints an independent accredited verifier and passes the result on. The verifier issues a report with an opinion on whether the data is satisfactory, and the report can include a summary for each CBAM good the installation makes. The installation then gives the importer either the full report or the summary for the goods it bought, and the importer keeps that document as evidence for its CBAM return.

Where no verified figure exists, the importer uses HMRC's default value, which carries a 10 per cent mark-up in every sector except fertiliser.

Which year's data counts

For goods imported in 2027, the importer uses verified data for the 2027 calendar year, and where that is not yet available it may use verified data for 2026. From 1 January 2028, the importer can use the most recently verified figure from either of the two calendar years before the import. An installation that gets its 2026 data verified can therefore offer its UK customers real figures from the first day of the scheme.

Who can verify

A verifier must be accredited against the CBAM requirements and the international verification standards ISO/IEC 17029 and ISO 14065, with an accreditation scope that covers the installation's production processes, and it must be independent of the installation. The accreditation body must be a full member of the Global Accreditation Cooperation, comply with ISO/IEC 17011 and have been peer evaluated for those two standards. It may accredit verifiers in its own country, and in another country only where that country has no eligible body or its body does not accredit CBAM verifiers. Each accreditation body must publish its list of accredited CBAM verifiers in English.

What the verifier will check

The technical guide sets the materiality level at 5 per cent of a good's total emissions intensity. An error that moves the intensity by more than that must be treated as material, and the verifier can still judge a smaller error material. The verifier must make a physical site visit to the installation at least once during the verification. It can waive the visit, or hold it virtually, only where, among other conditions, it has itself visited in the two preceding monitoring periods and nothing significant has changed since. A virtual visit is also allowed where serious, unforeseeable circumstances such as travel restrictions prevent attendance. In practice, an installation's first UK CBAM verification will normally include a physical visit. The guide also expects each installation to keep its monitoring plan as a single, live document setting out its methods and data flows.

Feedback by 13 November

HMRC describes the technical guide as supplementary and may update it before 1 January 2027. It invites technical feedback by 13 November 2026 to cbampolicyteam@hmrc.gov.uk, with "MRV technical guidance feedback" in the subject line. Operators and verifiers who find a method that does not fit their process should say so now.

What to do now

Importers should ask their main overseas suppliers whether they will monitor emissions to these rules, which verifier they plan to use and when the site visit is booked. Suppliers already preparing EU CBAM data should check that their verifier holds, or is seeking, accreditation for the UK scheme, because HMRC's guidance sets its own accreditation route and does not say that an EU CBAM accreditation counts.

CBAM-Assured trains operators, importers and consultants in CBAM monitoring, reporting and verification, and helps installations prepare data that stands up to a verifier's visit; contact us to plan your first UK verification.