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With Mexico's approval in January 2026, the UK's accession to the Comprehensive and Progressive Agreement for Trans-Pacific Partnership (CPTPP) is now binding on all parties except Canada. This marks the culmination of a five-year negotiation process that began with the UK signing the protocol to become a party to the CPTPP in July 2023.
Although the UK already has bilateral investment treaties (BITs) in place with several CPTPP members, accession to the agreement brings additional benefits. It establishes tariff-free trade routes, introduces modern rules for digital commerce, and provides a framework addressing supply-chain resilience. These arrangements extend not only to the UK but to all CPTPP members, potentially affecting their economic relationships and respective positions in global trade.
The UK's BITs with CPTPP members remain in force, given their independence and autonomy from other treaties. As a result, the conclusion of the CPTPP does not automatically terminate those BITs unless the parties expressly agree to do so. In the context of the UK's accession to the CPTPP, the available accession documents and the structure of the CPTPP suggest that BITs and the CPTPP may operate in parallel, allowing investors to choose which regime to rely on for dispute settlement or investment protection.
However, once the CPTPP – including its investment chapter – enters into force between the UK and other member states, the practical relevance of existing BITs may evolve. Chapter 9 of the CPTPP sets out the rules and substantive protections for investor-state dispute settlement (ISDS), which apply to investments made both before and after the CPTPP takes effect. This means that the protections offered under the CPTPP and those under BITs may overlap. How this overlap is managed would depend on the approach taken by each signatory state, which may choose to: (a) allow both regimes to operate in parallel, (b) review and disapply a BIT to avoid duplication or conflict with the CPTPP, or (c) terminate or renegotiate a BIT if they consider the CPTPP's investment protections to be sufficient.
In this evolving landscape, investors may wish to assess investment structures and should remain alert to any treaty adjustments, so as to make informed choices about the most advantageous treaty protections.
*Special thanks to International Law ClerkPerla Salgado for contributing to this GT Alert.
The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.
