Britain will formally apply Monday to join the Pacific free trade area not long after quitting the European Union's single market.

International Trade Secretary Liz Truss will formally request for Britain to be admitted to the Comprehensive and Progressive Agreement for Trans-Pacific Partnership (CPTPP) in meetings with ministers from Japan and New Zealand.

The bloc represents a market of half a billion people and roughly 13.5 percent of the global economy.

The move comes a year after Britain left the EU, ending more than 40 years of membership, and after five years of complex trade discussions with the bloc.

Ahead of the formal application, British Prime Minister Boris Johnson said the potential new partnership would "bring enormous economic benefits for the people of Britain".

"Applying to be the first new country to join the CPTPP demonstrates our ambition to do business on the best terms with our friends and partners all over the world and be an enthusiastic champion of global free trade," he said.

Negotiations between the UK and the partnership -- which represents 11 Pacific Rim nations including Australia, Canada, Chile, Japan, Mexico and Vietnam -- are expected to start this year, the trade department said.

But opposition Labour party shadow international trade secretary Emily Thornberry questioned the lack of transparency surrounding the pact.

After five years of debate over Brexit trade agreements, she said people would question the British government's decision "to rush into joining another one on the other side of the world without any meaningful public consultation at all."

"At present, Liz Truss cannot even guarantee whether we would have the right to veto China's proposed accession if we join the bloc first," she said.

Boris Johnson wants to join a Pacific free trade bloc that Donald Trump snubbed
Boris Johnson wants to join a Pacific free trade bloc that Donald Trump snubbed GETTY IMAGES NORTH AMERICA / JUSTIN SULLIVAN

Truss said joining the CPTPP would offer "enormous opportunities".

Britain has already made agreements with CPTPP members such as Japan and Canada in the wake of Brexit and, according to British media reports, CPTPP nations accounted for around eight percent of UK exports in 2019.

Truss said the deal would mean lower tariffs for car manufacturers and whisky producers, and would also deliver "quality jobs and greater prosperity for people here at home".

Speaking to Sky News on Sunday, Truss praised the arrangements of the CPTPP in comparison to the EU, where Britain was subject to bodies like the European Court of Justice.

"There aren't the strings attached so we wouldn't have a court making judgments, we wouldn't have any control over our borders lost, we wouldn't be paying any money in," she said.

The CPTPP was launched in 2019 to remove trade barriers among 11 nations in the Asia-Pacific region and counter China's growing economic influence.

The partnership is an updated version of a deal originally backed by former US president Barack Obama.

The United States pulled out of the agreement under Donald Trump's presidency -- turning away from what he viewed as unfavourable multilateral deals.