129 Days to CBAM: HMRC Lays Secondary Legislation for UK Carbon Tax

Exactly 129 days remain until the UK Carbon Border Adjustment Mechanism (CBAM) takes effect on 1 January 2027, and HM Revenue & Customs (HMRC) has now laid the critical secondary legislation required to govern its administration. This regulatory package, introduced to Parliament following the Finance Act 2026, marks the transition from theoretical policy to enforceable customs law. For trade compliance professionals, the window for preparation is closing rapidly as the government formalises how carbon prices will be calculated and relieved at the border.

The CBAM Regulatory Framework Takes Shape

The first package of secondary legislation, laid on 13 July 2026 and detailed in recent guidance, covers the essential administrative provisions for the UK CBAM. According to CBAM's Definitive Period Is Here: The European Commission's New Guidance — and the UK's Own Carbon Border Tax Right Behind It, these regulations define the rate calculation methods, carbon price relief rules, and transitory arrangements for importers. A second set of draft regulations focusing on emissions verification is expected to follow shortly.

Crucially, the UK version of CBAM contains significant structural differences from the European Union’s equivalent system. Businesses operating across both jurisdictions cannot simply replicate their EU compliance models for the UK market. HMRC’s approach to carbon price relief and the specific list of covered goods requires a bespoke data strategy to avoid double taxation or non-compliance penalties. The Finance Act 2026 provides the legal bedrock, but these new statutory instruments provide the granular detail that customs brokers need to configure their software and reporting protocols.

The September 15 Modernisation Deadline

While CBAM dominates the long-term horizon, a more immediate deadline is fast approaching. The joint HMRC and HM Treasury call for evidence, titled "Modernising the UK Customs Regime," is set to close on 15 September 2026. As noted in Modernising the UK Customs Regime - GOV.UK, this consultation is one of the most significant policy reviews since the UK’s exit from the European Union. It seeks industry views on trade digitalisation, the reduction of mandatory data fields in safety and security declarations, and the overall evolution of the Customs Declaration Service (CDS).

HMRC is particularly interested in how modernised trading practices can reduce the administrative burden on the 91 million declarations processed annually. According to HMRC Opens Call for Evidence on Modernising the UK Customs Regime, the government is looking for concrete evidence on how to streamline the intermediary market and improve the user experience for freight forwarders. Failure to respond by the September deadline means missing a primary opportunity to shape the next decade of UK customs infrastructure.

AI and the Transformation Roadmap

Parallel to these legislative shifts, HMRC has released its 2026 Transformation Roadmap update, which signals a heavy investment in artificial intelligence. A key highlight for TCSA members is the planned overhaul of the Online Trade Tariff. As reported in Inside HMRC's 2026 Transformation Roadmap: CDS, GVMS, and the AI Push Reshaping UK Customs, the tool will move from a static reference resource to an AI-assisted, journey-based service. This is intended to help declarants navigate complex commodity codes and duty rates with greater accuracy.

The roadmap also reaffirms HMRC’s commitment to the resilience of the Goods Vehicle Movement Service (GVMS) and CDS. While no immediate replacement for CDS is on the horizon, the department is focusing on digital-first interactions, with a target of 78% of customer interactions being digital by the end of the 2026-2027 period. For compliance officers, this means that internal processes must increasingly align with automated, data-driven government systems.

What this means for you

• Review the CBAM Secondary Legislation: Download the administrative provisions laid on 13 July 2026 to identify specific carbon price relief rules that apply to your product categories before the 1 January 2027 start date.
• Submit Evidence by 15 September: Ensure your organisation provides feedback to the "Modernising the UK Customs Regime" call for evidence, specifically addressing the data redundancies in import and export declarations.
• Audit Supply Chain Carbon Data: Begin collecting verified emissions data from suppliers now; the structural differences between UK and EU CBAM mean that EU-standard reports may not be sufficient for HMRC requirements.
• Monitor the Online Trade Tariff AI Beta: Prepare for the transition to the new journey-based tariff tool by reviewing internal classification workflows and ensuring they can integrate with AI-assisted government interfaces.

The convergence of green trade policy through CBAM and the digital-first push of the HMRC Transformation Roadmap represents a fundamental shift in the UK’s trading identity. As we move toward 2027, the role of the customs professional is evolving from a transactional filer to a strategic data manager. Staying ahead of these legislative deadlines is no longer just about compliance—it is about maintaining a competitive edge in a rapidly modernising global market.