UK CBAM · Two regimes, one supply chain
UK CBAM is not EU CBAM with a different flag.
Different sectors, different start dates, different filing rhythm, different authority, and — for now — a different output format. If you import into both, you run two obligations on two clocks. This page sets them side by side, each line cited to the instrument.
One year apart, and aligned on almost nothing else
Obligations are live. The first annual declaration, covering calendar year 2026, is due by 31 May 2027.
Reg (EU) 2023/956, Art. 36(2)(b) · Art. 6(1)The first accounting period runs the full twelve months of 2027. The first return and the first payment are both due by 31 May 2028.
FA 2026 s.158(1) · SI 2026/830 reg 2(3), 2(4)Scope and timing
Six. Cement, electricity, fertilisers, iron and steel, aluminium, and hydrogen under chemicals.
Reg (EU) 2023/956, Annex IFive. Aluminium, cement, fertilisers, hydrogen, and iron and steel.
FA 2026 s.143(3) · Sch 16In scope. CN 2716 00 00 is listed in its own right, and imported electricity is declared in megawatt-hours.
Reg (EU) 2023/956, Annex I · Art. 6(2)(a)Out of scope. No electricity commodity code appears in Schedule 16, and the government response says so in terms.
FA 2026 Sch 16 · Government response, 30 Oct 2024, paras 2.4, 2.16Inside the definition of embedded emissions — except for the goods listed in Annex II, where only direct emissions are taken into account.
Reg (EU) 2023/956, Art. 3(22) · Art. 7(1) · Annex IIOutside it. The system boundaries document supporting the secondary legislation covers direct emissions only, and inclusion is stated as delayed until 2029.
SI 2026/809 reg 2 · System boundaries document v1.00 · HM Treasury factsheet1 January 2026. That is the date the declaration, calculation and certificate articles begin to apply.
Reg (EU) 2023/956, Art. 36(2)(b)1 January 2027, for goods imported into the United Kingdom on or after that date.
FA 2026 s.158(1)Annual. One declaration by 31 May each year, covering the preceding calendar year.
Reg (EU) 2023/956, Art. 6(1)Twelve months for 2027, then quarterly — periods ending at the end of March, June, September and December.
SI 2026/830 reg 2(3) · FA 2026 Sch 17 para 6(2)Obligation and output
The EU importer
Reg (EU) 2023/956, Art. 5The UK importer
FA 2026 s.146(1), (2)The CBAM registry — the standardised electronic database the Commission maintains.
Reg (EU) 2023/956, Art. 6(1) · Art. 14(1)HMRC. The Commissioners are responsible for the collection and management of CBAM.
FA 2026 Sch 17 paras 1(1), 2(1)31 May 2027, for calendar year 2026.
Reg (EU) 2023/956, Art. 6(1)31 May 2028, for the accounting period ending 31 December 2027.
SI 2026/830 reg 2(4) · FA 2026 Sch 17 para 7(2)(a)CBAM certificates, surrendered through the registry by 31 May, first time in 2027 for 2026.
Reg (EU) 2023/956, Art. 22(1)A tax payment — the sectoral domestic price for the quarter, multiplied by the tonnes of embodied emissions.
FA 2026 s.149(1), (2) · SI 2026/809 regs 3, 4Quantities, embedded emissions, the number of certificates to surrender, and copies of verification reports from accredited verifiers.
Reg (EU) 2023/956, Art. 6(2)Per good — the 8-digit commodity code, the weight, the carbon price relief and the place of origin, with a declaration of truth.
SI 2026/802 reg 10(1), 10(2)Where the two regimes diverge most
Both regimes prescribe what a return must contain. Only one of them has told you what the file looks like. SI 2026/802 sets out the required contents of a UK CBAM return; HMRC has not published a data schema for it. Until it does, no one can produce a validated UK return file — Carbon Mandate included. What carries across today is the harder half: turning unstructured supplier data into a structured, cited, audit-ready emissions record. The output adapter follows the schema when the schema exists.
SI 2026/802 reg 10 · Reg (EU) 2023/956, Art. 6(6)Not yet settled
The regulation fixes what the declaration must contain, then leaves its standard format — and the procedure for submitting it through the CBAM registry — to Commission implementing acts.
Reg (EU) 2023/956, Art. 6(2), Art. 6(6)Regulation 10 fixes what a UK return must contain. A notice published in draft on 13 July 2026 requires returns to be submitted using the HMRC CBAM service through a Government Gateway account, and takes effect on 1 January 2027. It specifies the service, not a file format.
SI 2026/802 reg 10 · FA 2026 Sch 17 para 7(4) · force of law notice (draft), 13 Jul 2026TWO REGIMES · ONE PREPARATION LAYER
20 minutes. We prepare a real CBAM file in front of you.
No slides. Live validation against your sector.