UK Publishes Default Emissions Values for 2027 Carbon Border Tax

HM Revenue and Customs published default emissions values on October 16 for the goods the UK's Carbon Border Adjustment Mechanism will cover, fourteen months before the import levy begins on January 1, 2027. The benchmarks give importers a reference point for calculating carbon tax liabilities when verified emissions data does not exist.

The values cover selected products in five sectors: aluminium, cement, fertiliser, hydrogen, and iron and steel. Importers can enter the published figures in CBAM returns in place of verified actual emissions data, the government guidance states. HMRC released the numbers alongside instructions on how businesses should apply them.

The Treasury set out the next implementation steps in a written statement to Parliament, including how the default figures will feed into the calculation of importers' liabilities.

What does this change for importers?

The defaults offer a practical route to estimate emissions where product-specific verified data is unavailable. A trader bringing aluminium or steel into the UK without supplier emissions documentation can now price the exposure rather than wait. Businesses still need to determine which goods fall within scope and how the applicable rules shape their reporting and tax calculations.

The scheme targets carbon leakage: the risk that production shifts to countries with weaker climate policies or lower carbon costs. The charge will reflect the emissions embedded in covered goods, alongside relevant carbon pricing adjustments. In practice, that means suppliers with low-carbon processes and credible documentation hold a pricing advantage once the levy starts.

A parallel track to Brussels

The UK mechanism follows the broad architecture of the European Union's carbon border scheme, though London is drafting its own rules. The EU's definitive CBAM phase began in 2026, tightening scrutiny of carbon costs across international industrial supply chains. UK importers supplying both markets will face two reporting regimes with separate methodologies, a compliance burden the default values only partially relieve.

The October 16 publication marks another step toward the UK's new carbon pricing regime. As the start date approaches, importers and suppliers will concentrate on emissions documentation, sourcing decisions, and the financial exposure the mechanism creates. Firms that track those variables now will face fewer surprises when the first CBAM returns fall due.

The decisive milestone sits ahead: the first chargeable imports on January 1, 2027, when the defaults stop being a planning tool and become a tax liability.