On 14 August 2026, the European Commission published a set of ten guidance documents aimed at operators outside the EU, authorised CBAM declarants, and verifiers — all designed to help them navigate the definitive period of the Carbon Border Adjustment Mechanism (CBAM). It reads like a routine administrative release, but it marks a genuine change in what CBAM now costs to get wrong.
The transitional period, which ran from October 2023 to the end of 2025, asked importers to report embedded emissions on a quarterly basis — with no certificates to buy and no direct financial penalty tied to the figures themselves. That grace period ended on 1 January 2026. From this year, CBAM has real teeth: registration as an authorised declarant, certificate purchase, annual declarations, and verified emissions data that determine an actual financial liability at the EU border.
For UK businesses, the timing carries a second layer of urgency. The UK is building its own Carbon Border Adjustment Mechanism, due to take effect on 1 January 2027 — and it does not mirror the EU’s approach in either mechanics or scope. Trade and compliance teams handling carbon-intensive goods now have two separate carbon border regimes to track, on two different timelines, administered by two different bodies, calculating liability in two different ways.
Under the transitional regime, CBAM was essentially a data-collection exercise. Importers of goods in scope submitted quarterly reports estimating embedded emissions, using either actual supplier data or default values — and there was no certificate to buy and no sum to pay.
Since 1 January 2026, that has changed. EU importers, or their indirect customs representatives, who bring more than 50 tonnes of CBAM goods into the EU in a year must now apply for the status of authorised CBAM declarant through the National Competent Authority (NCA) in their country of establishment. Only an authorised declarant may import CBAM goods above the threshold, and only an authorised declarant can access the CBAM Registry — the system through which certificates are bought and declarations are filed.
Authorised declarants purchase CBAM certificates priced against the auction price of EU Emissions Trading System (ETS) allowances, calculated as a quarterly average during 2026 and moving to a weekly average from 2027. Once a year, the declarant reports the actual embedded emissions in their imports and surrenders the corresponding number of certificates, with a reduction available where a carbon price has already been paid during production abroad.
Where the underlying emissions data cannot be verified to the standard the definitive regime now expects, the guidance is clear: declarants fall back on conservative default values — which tend to produce a higher certificate obligation than accurate, supplier-verified figures.
The 14 August package is split into four general guides and six sector-specific ones, each of the latter with worked examples. The full series sits on the Commission’s CBAM legislation and guidance page.
| Guidance | What It Covers |
|---|---|
| No. 1 | CBAM’s compliance cycle, roles, responsibilities, milestones and exemptions for operators outside the EU. |
| No. 2 | A shorter roadmap aimed specifically at non-EU operators, pointing to where the detail on emissions monitoring sits across the wider series. |
| No. 3 | Calculation of embedded emissions and the monitoring obligations that apply to producers of CBAM goods. |
| No. 4 | How the adjustment for free allocation under the EU ETS is applied to the number of certificates an authorised declarant must surrender. |
| No. 5a–5f | Sector-by-sector production processes, value chains and monitoring considerations, each with worked examples — covering cement, hydrogen, fertilisers, iron and steel, aluminium, and electricity. |
The Commission has been explicit about why the timing matters: businesses need to be ready for verification of their emissions data and have monitoring processes robust enough to use actual values, rather than defaults, for 2026 imports.
That single point deserves particular attention from UK exporters. A UK producer of iron, steel, aluminium, cement, fertiliser or hydrogen does not itself surrender certificates or file a CBAM declaration — that obligation sits with the EU importer, as the authorised declarant. But the new guidance is aimed squarely at operators like these, because it is their monitoring plans and their emissions data that determine whether their EU customer pays for accurate, lower embedded emissions or defaults to the Commission’s more conservative published figures.
The Commission names three audiences:
That third group matters more under the definitive regime than it did during the transitional period, when self-reported estimates were largely accepted at face value. From 2026, the numbers behind a CBAM declaration are expected to hold up to verification — which puts pressure on both the quality of the underlying monitoring plan and the consistency of the data trail supporting it, from production records through to the commercial and customs documentation that accompanies the shipment.
The UK’s own Carbon Border Adjustment Mechanism takes effect on 1 January 2027 under the Finance Act 2026, which received Royal Assent in March 2026. On 13 July 2026, HMRC laid the first package of secondary legislation before Parliament — covering administrative provisions, the rate calculation and carbon price relief rules, and transitory arrangements — with a further set of draft emissions and verification regulations still to follow from a second consultation. The structural differences from the EU version are significant enough that businesses trading across both markets cannot simply apply one compliance model to both.
| EU CBAM | UK CBAM | |
|---|---|---|
| Mechanism | Certificate purchase and surrender through the CBAM Registry. | A tax administered by HMRC: embodied emissions × sector-specific UK CBAM rate, minus any qualifying overseas carbon price already paid. |
| In force | Definitive period from 1 January 2026. | 1 January 2027 (Finance Act 2026). |
| Threshold | Mass-based: more than 50 tonnes of CBAM goods imported per year. | Value-based: £50,000, tested forward (next 30 days) and backward (preceding 12 months, checked on the first day of each month). |
| Liable party | The authorised CBAM declarant (the EU importer or their indirect customs representative), authorised via the NCA. | Generally whoever’s name appears on the customs declaration. |
| Sectors | Cement, hydrogen, fertilisers, iron and steel, aluminium — and electricity. | Aluminium, cement, fertilisers, hydrogen, iron and steel. Electricity is excluded; glass and ceramics were dropped from the original proposal. |
| Carbon price basis | Certificates priced on EU ETS auction averages — quarterly during 2026, weekly from 2027. | Rate set quarterly from the average UK ETS auction price for the preceding quarter, adjusted for free-allowance coverage per sector (free allocation phased out over nine years from 2027 for CBAM-covered sectors). |
| Reporting | Annual CBAM declaration with certificate surrender. | First accounting period = the full 2027 calendar year, with the first return and payment due by 31 May 2028; quarterly returns from the second period. Registration expected to open by 1 January 2028. |
A business trading electricity-intensive goods into both markets needs to know the electricity difference specifically, because it is not intuitive from the EU rules alone. And note the registration timing carefully: UK registration is expected to open by 1 January 2028, but the underlying liability and record-keeping obligations begin with the first accounting period — the full 2027 calendar year. HMRC’s guidance on working out a registration date is available directly on GOV.UK, alongside the wider collection of CBAM registration guidance.
There is a longer-term development worth watching. At the UK–EU Summit in May 2025, both sides committed to working toward linking their emissions trading schemes, and in November 2025 the EU Council authorised the Commission to begin formal negotiations, which opened in January 2026. If that linkage is agreed, it could lead to mutual CBAM exemptions between the UK and EU — sparing goods moving between the two markets from carbon border charges on both sides.
The UK government’s own estimate suggests ETS linkage could save UK industry in the region of £800 million by 2030. Nothing here should be treated as settled — businesses exporting to the EU should continue planning for full EU CBAM compliance in the meantime — but it is a live negotiation that could materially change the compliance picture for UK producers within the next few years.
The practical starting point is the same on both sides of the Channel: know exactly which of your goods fall inside CBAM’s scope by commodity code, because that classification decision now drives a genuine financial consequence rather than a reporting formality.
The thread connecting both regimes is data quality at the point of declaration. Commodity codes, net mass, country of origin, and customs value are not just CDS or CBAM inputs in isolation; they are the same figures that need to reconcile across the commercial invoice, the customs declaration, and whatever CBAM reporting sits alongside it. Inconsistencies between those documents are exactly what a verifier, an NCA, or HMRC will query first.
Every CBAM assessment — on either side of the Channel — starts with the customs data underneath it: a correct commodity code, an accurate net mass, a defensible country of origin, and a customs value that reconciles with the commercial documents. Those are precisely the fields validated in real time through CDUK’s import declarations and wider CDS declaration workflows, making the platform the natural place to build the data discipline both carbon border rules will test. And as HMRC finalises how the UK CBAM will operate ahead of 2027, Customs Declarations UK is tracking the rollout closely so that support for customers keeps pace as the requirements take shape.
CBAM has moved from a compliance exercise businesses could treat as background administration to one with a direct line to cost. The Commission’s August 2026 guidance package is a signal that the EU expects operators, declarants, and verifiers to be working from real data now, not estimates. UK businesses face that reality twice: once for goods they already send into the EU, and again from January 2027 for goods they bring into Great Britain under a UK regime built on different mechanics and a different scope.
Getting the underlying customs data right, consistently, and early is the common thread that makes both CBAM timelines manageable.