UK CBAM Guide 2027: How the Tax-Based Carbon Border Mechanism Works

The UK CBAM launched on January 1, 2027, establishing a direct tax on the embedded carbon emissions of goods imported into Great Britain across 6 industrial sectors: steel, aluminium, ceramics, cement, fertilizers, and hydrogen. Unlike the EU CBAM, which operates through a certificate-based mechanism priced at the EU Emissions Trading System auction price, the UK carbon border adjustment is a direct financial charge administered by HMRC, payable by the UK importer at the point of customs clearance. Understanding the distinction between these two mechanisms is essential for any business importing into either market or operating across the UK-EU trade corridor.

This guide covers how the UK CBAM tax is calculated, which sectors and goods fall within scope, how UK importers register and comply, and how the mechanism differs structurally from the EU CBAM certificate system.

What Is the UK CBAM?

The UK CBAM is a direct tax on the carbon content of specified imported goods, paid by UK importers to HMRC, calculated by reference to the embedded greenhouse gas emissions in those goods and a carbon price reflecting the UK Emissions Trading Scheme (UK ETS).

The UK carbon border adjustment mechanism covers goods imported into Great Britain from countries where production-related carbon costs are lower than those faced by equivalent UK producers operating under the UK ETS. Its primary purpose is to prevent carbon leakage, the displacement of CO2 emissions from the UK (where they carry a cost under the UK ETS) to jurisdictions without equivalent carbon pricing, and to ensure that UK producers do not face an unfair competitive disadvantage against lower-cost imports.

The UK CBAM differs from the EU CBAM in three fundamental ways. First, it is a tax, not a certificate obligation. Second, it is administered by HMRC as a tax authority, not by a national competent authority managing a certificate registry. Third, the price reference is the UK ETS carbon price, which operates independently from the EU ETS and has not been linked to it as of January 2027.

The mechanism took effect January 1, 2027, following a consultation period that ran from 2023 through 2024, primary legislation enacted through the Finance Act, and secondary legislation defining scope, calculation methodology, and administrative procedures. The 6 sectors brought into scope at launch are listed below, with ceramics representing the most notable divergence from EU CBAM sector coverage.

How the UK CBAM Tax Is Calculated

UK CBAM liability is calculated by multiplying the embedded greenhouse gas emissions in the imported goods by the UK ETS carbon price, then applying a deduction for any carbon price already paid in the country of origin. The 3 components of the calculation are described below.

Component 1: Embedded emissions. The quantity of greenhouse gas emissions, expressed in tonnes of CO2 equivalent (tCO2e), associated with the production of the imported goods. Importers can use verified actual emissions data supplied by the overseas manufacturer, or default emission values published by HMRC for situations where actual data is unavailable.

Component 2: The UK ETS carbon price reference. The UK government publishes a quarterly carbon price reference value derived from UK ETS auction prices. This value is used to convert embedded emissions into a monetary liability. The UK ETS price as of January 2027 sits independently of EU ETS pricing, meaning the CBAM tax rate in the UK can diverge from the effective cost of EU CBAM certificates even for the same physical goods.

Component 3: Origin country carbon price deduction. Where a carbon price has been paid in the country of export, importers can apply a deduction to reduce UK CBAM liability. The deduction reflects the principle that goods should not be taxed twice for the same emissions. The rules for qualifying deductions, including requirements for the foreign price to be legally binding and effectively enforced, broadly mirror the approach taken under EU CBAM Article 9, though the specific administrative procedures differ.

The formula produces a net UK CBAM tax liability per import consignment. Importers must account for this within their customs and tax reporting to HMRC.

Caption: The UK carbon border adjustment tax is calculated from three components: embedded emissions, the UK ETS price reference, and any qualifying carbon price paid in the country of origin.

Which Sectors Does the UK CBAM Cover?

The UK CBAM covers 6 sectors at launch on January 1, 2027. The 6 sectors in scope are listed below.

The 6 UK CBAM sectors and their key characteristics are summarized in the table below:

Ceramics represents the most significant difference in sector coverage between the UK CBAM and the EU carbon border mechanism. The EU CBAM, established by Regulation (EU) 2023/956, covers 6 sectors: iron and steel, cement, aluminium, fertilizers, electricity, and hydrogen. Electricity is covered by EU CBAM but is not included in the UK CBAM at launch. Ceramics, which encompasses tiles, sanitaryware, and refractory products, is covered by the UK CBAM but falls outside EU CBAM scope.

These sector differences create operational asymmetry for businesses importing into both markets. A ceramics importer selling into the UK faces UK CBAM liability with no equivalent EU CBAM charge. A generator exporting electricity to the EU via interconnectors faces EU CBAM scope with no UK CBAM equivalent on that product.

How UK CBAM Differs from EU CBAM

The UK carbon border adjustment and the EU CBAM share the same policy purpose: preventing carbon leakage from domestic carbon pricing systems. The 2 mechanisms differ fundamentally in their legal structure, administrative process, and compliance obligations.

The EU CBAM, established under Regulation (EU) 2023/956 and amended by Regulation (EU) 2025/2083 (the Omnibus simplification), operates as a certificate-based mechanism. EU importers must obtain authorization as an authorized CBAM declarant, purchase CBAM certificates through the CBAM Registry (the Common Central Platform, with certificate sales beginning February 1, 2027), hold at least 50% of cumulative embedded emission certificates at each quarter-end, and submit an annual CBAM declaration by September 30 of the year following import. The EU CBAM certificate price is derived from weekly EU ETS auction clearing prices.

For a full explanation of how EU CBAM certificates are purchased, held, and surrendered, see the EU CBAM guide.

The UK CBAM operates as a direct tax. There is no certificate to purchase, no registry account to maintain, and no quarterly holding requirement equivalent to the EU CBAM rule. UK importers pay the tax through their existing HMRC customs and tax reporting infrastructure. The administrative pathway is therefore distinct and, for importers already familiar with UK tax compliance through HMRC, more recognizable than the certificate registry model.

The table below summarizes the 8 primary structural differences between UK CBAM and EU CBAM:

The certificate-based approach used by the EU CBAM creates specific compliance obligations, including the CBAM certificates system, that have no direct equivalent in the UK regime. EU importers who are also UK importers must therefore maintain parallel compliance processes under two distinct regulatory frameworks.

UK CBAM Consultation and Legislative Background

The UK CBAM consultation process ran across 2023 and 2024, with the UK government publishing its design framework for a carbon border adjustment mechanism following the UK's exit from the EU ETS and the establishment of a standalone UK ETS. The consultation addressed 5 core design questions: sector scope, emissions calculation methodology, carbon price deduction rules, the treatment of least developed countries (LDCs), and administrative integration with existing HMRC customs systems.

The UK government confirmed LDC exemption as a feature of the UK CBAM, meaning goods imported from countries classified as least developed countries under OECD/DAC criteria are exempt from UK CBAM liability. This LDC exemption has no direct equivalent in the EU CBAM, which determines exemptions based on whether the exporting country's carbon price system has been assessed as equivalent (under the Annex III framework), not on development status.

The Finance Act enacted primary CBAM legislation, with secondary legislation and HMRC guidance providing the detailed rules for calculation methodology, importer registration, default values, and deduction procedures. HMRC administers the UK CBAM as a tax matter, which means appeals and disputes follow standard UK tax tribunal procedures rather than the customs and environmental enforcement routes that apply under EU CBAM.

What UK CBAM Means for Importers

UK importers of goods in the 6 covered sectors face 4 primary obligations under the UK carbon border adjustment mechanism.

The 4 UK CBAM obligations for importers are as follows:

1. Register with HMRC as a UK CBAM liable person. Registration requirements apply to importers whose annual imports of covered goods exceed the de minimis threshold. The UK CBAM de minimis provisions apply at the level of annual import value rather than the 50-tonne annual mass threshold used under EU CBAM (Article 2(3a), as amended by Regulation (EU) 2025/2083).

2. Obtain embedded emissions data from overseas suppliers. Importers can use verified actual emissions data from the production installation or, where actual data is unavailable, apply HMRC-published default values. Importers using default values face a higher effective tax rate, as defaults are set conservatively. Engaging suppliers to provide actual emissions data is therefore financially advantageous for most high-volume importers.

3. Calculate and report UK CBAM liability through HMRC's customs and tax filing processes. This differs from the EU system, where the authorized CBAM declarant submits a dedicated CBAM declaration to the competent authority. UK CBAM reporting integrates into existing HMRC systems, which reduces the need for a parallel specialized registry account but requires importers to adapt their customs data flows to include carbon content information.

4. Pay the UK CBAM tax on the schedule determined by HMRC. Penalties for non-compliance are set by UK tax legislation and enforced by HMRC using standard UK tax authority powers. The penalty structure differs from the EU CBAM penalties of €100 per tonne CO2e for authorized declarants failing to surrender sufficient certificates and €300 to €500 per tonne CO2e for unauthorized importers.

Caption: UK CBAM importers follow a four-step compliance process: HMRC registration, emissions data collection, liability calculation and reporting, and tax payment.

UK CBAM Default Values and Emissions Verification

Default values under the UK CBAM serve the same structural purpose as EU CBAM default values: they provide a fallback emissions figure for importers who cannot obtain verified actual data from their overseas suppliers. UK default values are published by HMRC by sector and country of origin, and they are set at levels that create a financial incentive to use actual data where possible.

The verification requirements for actual emissions data under UK CBAM follow principles broadly consistent with those used in the EU CBAM framework, requiring third-party verification of the monitoring methodology and emissions figures reported by the overseas production installation. The specific accreditation requirements for UK CBAM verifiers are established through HMRC guidance and UK conformity assessment standards.

Suppliers in the 6 UK CBAM sectors who currently report emissions data to EU importers for EU CBAM purposes can, in principle, use compatible emissions measurement approaches for UK CBAM reporting. The calculation methodologies are not identical, and importers must confirm that their supplier's emissions data meets UK CBAM requirements specifically. Data prepared exclusively to meet EU CBAM implementing regulations, particularly IR (EU) 2025/2547 on calculation methodology, may require supplementary documentation to satisfy UK CBAM requirements.

UK CBAM and the Double-Payment Risk

One of the most significant unresolved issues at the intersection of UK CBAM and EU CBAM is the potential for double carbon pricing on goods that cross both the UK and EU borders, or for UK manufacturers who import CBAM-covered inputs that are then further processed and exported to the EU.

The double-payment scenario arises in a specific set of trade flows. A UK manufacturer who imports steel from India pays UK CBAM on the embedded emissions of that steel. When the UK manufacturer's finished product (incorporating that steel) is exported to the EU, the EU importer may face EU CBAM liability on the embedded emissions of the steel component, depending on product classification. The UK CBAM charge paid by the UK manufacturer on the input does not automatically qualify for an Article 9 deduction under EU CBAM, because Article 9 requires the carbon price to be paid in the country of origin of the exported good, not by an intermediate processor in a third country.

Whether UK ETS costs incurred by UK producers qualify for an Article 9 deduction against EU CBAM obligations is a separate and equally important question. The UK ETS operates independently from the EU ETS and has not been formally recognized as a qualifying equivalent scheme under EU CBAM Article 9 as of January 2027. UK exporters to the EU therefore face the risk of their EU customers bearing full EU CBAM costs even though the UK production process carries UK ETS costs. No bilateral UK-EU agreement on mutual recognition of carbon pricing for CBAM purposes exists as of this date.

How UK CBAM Relates to the UK ETS

The UK ETS is the UK's cap-and-trade carbon pricing system established following the UK's departure from the EU ETS at the end of 2020. UK ETS covers energy-intensive industries, power generation, and domestic aviation, requiring covered installations to hold UK ETS allowances equal to their annual verified emissions. The UK CBAM is designed to function as the trade-facing complement to the UK ETS, applying equivalent carbon cost pressure to imports of covered goods from countries without comparable pricing.

The relationship between UK ETS price and UK CBAM tax liability is direct: the quarterly carbon price reference published by HMRC for UK CBAM purposes is derived from UK ETS auction prices. As UK ETS prices rise, UK CBAM tax liability rises proportionally for imports with the same embedded emissions. This linkage mirrors the structural relationship between EU ETS prices and EU CBAM certificate costs, though the 2 carbon markets have moved independently since the UK ETS launched in January 2021.

UK domestic producers covered by the UK ETS, such as UK steelmakers and UK cement manufacturers, continue to face their UK ETS compliance costs on production. UK CBAM ensures that imported goods face a comparable cost. Free allocation within the UK ETS, similar in structure to EU ETS free allocation, is being phased out for UK CBAM-covered sectors in parallel with the CBAM's introduction, ensuring that the domestic carbon cost born by UK producers increases over time as UK CBAM applies equivalent pressure on imports.

What Is the UK CBAM's Relationship to EU CBAM Compliance?

Businesses operating across the UK-EU trade corridor face the practical challenge of managing parallel carbon border obligations under 2 separate regulatory regimes. The UK CBAM and EU CBAM have different sector scope, different administrative systems, different price references, and different compliance timelines.

Importers who operate in both markets require distinct compliance processes for each jurisdiction. The EU CBAM authorized declarant registration, required under IR (EU) 2025/486 with a 120-day decision timeline from a complete application, has no direct UK CBAM equivalent. The EU CBAM quarterly certificate holding requirement of at least 50% of cumulative embedded emissions since the start of the calendar year applies only to EU CBAM, not to UK CBAM. Similarly, the EU CBAM annual declaration deadline of September 30, covering the preceding calendar year, has no equivalent deadline in the UK CBAM reporting schedule, which integrates into standard HMRC customs filing timescales.

A detailed side-by-side comparison of both systems, including sector-by-sector scope overlap and administrative procedure differences, is covered in the UK CBAM vs EU CBAM comparison guide.

For importers already navigating EU CBAM authorized declarant status and the CBAM authorized declarant obligations in EU member states, adding UK CBAM compliance represents an incremental rather than equivalent workload, given that the UK tax model is administratively less intensive than the EU certificate registry model.

Frequently Asked Questions About UK CBAM

What is the UK CBAM start date?

The UK CBAM started on January 1, 2027, applying to imports of goods in 6 sectors: steel, aluminium, ceramics, cement, fertilizers, and hydrogen. The January 2027 start date positions UK CBAM as a parallel but distinct mechanism to EU CBAM, which entered its definitive phase on January 1, 2026, 12 months earlier.

Is UK CBAM a tax or a certificate system?

UK CBAM is a direct tax, not a certificate system. UK importers pay the UK CBAM charge to HMRC through tax reporting processes, without purchasing, holding, or surrendering any form of CBAM certificate. This is the single most important structural distinction between UK CBAM and EU CBAM: the EU mechanism requires importers to acquire certificates through the CBAM Registry, whereas the UK mechanism imposes a direct tax liability through HMRC.

Does UK CBAM cover the same sectors as EU CBAM?

No. UK CBAM and EU CBAM differ in their sector coverage across 2 goods categories. UK CBAM covers ceramics, which EU CBAM does not. EU CBAM covers electricity, which UK CBAM does not at launch. The remaining 4 sectors (steel, aluminium, cement, fertilizers) and hydrogen are covered by both mechanisms, though the detailed product-level scope may vary by CN code classification.

Who administers the UK CBAM?

HMRC administers the UK CBAM. This contrasts with EU CBAM, which is administered by national competent authorities in each of the 27 EU member states, with oversight by the European Commission's DG TAXUD. The HMRC administration model means UK CBAM disputes and appeals follow UK tax tribunal procedures, while EU CBAM enforcement and penalty decisions are made by the relevant member state competent authority.

Does the UK CBAM apply to goods from developing countries?

Goods imported from least developed countries (LDCs), as classified under OECD/DAC criteria, are exempt from UK CBAM. This LDC exemption has no equivalent in EU CBAM, which does not use development status as an exemption criterion. EU CBAM exemptions apply based on whether an exporting country's carbon pricing system qualifies under the Annex III framework (currently: Iceland, Liechtenstein, Norway, and Switzerland).

Can UK importers deduct carbon costs paid in the country of origin?

Yes. UK CBAM provides a deduction mechanism for qualifying carbon prices paid in the country of export, reducing UK CBAM tax liability. The foreign carbon price must be legally binding and effectively enforced to qualify. This deduction principle mirrors the EU CBAM Article 9 approach, though the specific calculation rules and qualifying criteria are established under UK legislation and HMRC guidance, not under Regulation (EU) 2023/956.

Is UK CBAM recognized under EU CBAM Article 9?

The UK ETS is not formally recognized as a qualifying carbon pricing scheme under EU CBAM Article 9 as of January 2027. No bilateral UK-EU agreement on mutual carbon pricing recognition exists. UK producers exporting to the EU therefore cannot guarantee that their EU customers receive an Article 9 deduction for UK ETS costs incurred during UK production. The CBAM declaration process for EU importers of UK goods must account for this uncertainty when assessing the net EU CBAM cost.

What happens if a UK importer does not comply with UK CBAM?

Non-compliance with UK CBAM is enforced by HMRC under standard UK tax authority powers, including financial penalties, interest on unpaid tax, and potential criminal liability for fraudulent declarations. The specific penalty rates are set by UK tax legislation. These differ from EU CBAM penalties: EU CBAM imposes €100 per tonne CO2e on authorized declarants who fail to surrender sufficient certificates, and €300 to €500 per tonne CO2e on unauthorized importers who bring CBAM goods into the EU without authorization.

UK CBAM: Sector and Trade Context

How Significant Is UK CBAM for Steel Importers?

Steel imports represent the largest volume category of UK CBAM-covered goods. The UK imports steel from countries including Turkey, India, South Korea, and China, all of which lack fully equivalent carbon pricing schemes that would qualify for a complete UK CBAM deduction. For blast furnace (BF-BOF) produced steel, embedded emissions run approximately 2.0 tCO2 per tonne of product. At a UK ETS carbon price of GBP 40 to GBP 70 per tonne CO2 (the range observed through 2025 and into 2026), UK CBAM adds GBP 80 to GBP 140 per tonne of BF-BOF steel imported without a carbon price deduction. Electric arc furnace (EAF) scrap-based steel, with embedded emissions of approximately 0.5 tCO2/t, produces UK CBAM liability of GBP 20 to GBP 35 per tonne at the same price range.

How Does UK CBAM Affect Aluminium Importers?

Primary aluminium imports face UK CBAM on direct embedded emissions, estimated at approximately 1.5 tCO2/t. Indirect emissions from electricity consumption in smelting, which can add 9 to 12 tCO2/t for coal-grid-powered production, are not priced under UK CBAM at launch (mirroring the EU CBAM treatment of aluminium indirect emissions). This means the UK CBAM tax on primary aluminium reflects only a fraction of the total lifecycle carbon footprint of coal-powered smelting. The CBAM regulation comparison article covers how EU CBAM handles this aluminium indirect emissions gap.

What Does UK CBAM Mean for Ceramics Importers?

Ceramics is the UK CBAM sector with no EU equivalent, making it a category where UK-specific compliance obligations arise independently of any EU CBAM exposure. The ceramics sector covers tiles, sanitaryware, tableware, technical ceramics, and refractory products, all manufactured through high-temperature kiln processes with significant direct CO2 emissions from both fuel combustion and calcination of raw materials. UK ceramics imports come primarily from Italy, China, Spain, and Turkey, all of which currently lack qualifying carbon pricing schemes for purposes of a UK CBAM deduction.