The decision on Wednesday by the 11 members of the Comprehensive and Progressive Agreement for Trans-Pacific Partnership (CPTPP) to allow Britain to formally start the process of joining the pact spells "win-win" for Britain, the CPTPP membership and the agreement itself. If its accession goes through, Britain would become the second largest economy in the grouping after Japan and its entry would expand the bloc's combined GDP by around 25 per cent in US dollar terms. As a member, Britain would gain easier access to a market that is roughly the same size as that of the European Union, which it was once a part of. However, the size of its trade with CPTPP members is barely one-sixth of what it is with the EU - which suggests there is much potential for Britain to expand its trade with the grouping.

But this will happen only gradually. Britain already has free trade arrangements in place with seven CPTPP members and is negotiating deals with two others, which means the additional economic gains from joining the partnership will be limited at first. However, Britain would be able to use inputs from across the CPTPP member-economies to build new supply chains. For example, as Britain's Secretary of State for International Trade Liz Truss explained, its automakers would be able to source parts from Japan to make cars and trucks in Britain and sell them tariff-free to Mexico, for example. Tariffs on some British exports would also come down faster under the CPTPP than under its bilateral trade pacts.