"This combat air aircraft, due to take to the skies by 2035, aims to harness next-generation technologies and become one of the world's most advanced, interoperable, adaptable and connected fighter jets in service globally," Britain's defence ministry said after the signing in Tokyo.

"The supersonic stealth jet will boast a powerful radar that can provide 10,000 times more data than current systems, giving a battle-winning advantage," the statement said.

The headquarters of the Global Combat Air Programme (GCAP) will be in Britain, under the agreement inked a year after the cooperation was first announced, the countries said.

The first chief executive will be Japanese and the head of the industry organisation will be from Italy, Britain's defence ministry said in a statement.

For Japan, which has announced a major increase in defence spending, the project represents a push to diversify away from its decades-long reliance on the United States for military hardware.

The cooperation pools resources from Britain and Italy's joint Tempest project with those of Japan's next-generation fighter plane F-X.

The treaty was signed by Japanese Defence Minister Minoru Kihara and his British and Italian counterparts Grant Shapps and Guido Crosetto.

"We live in a very complex time that is characterised by the presence of aggressive actors on the international stage... It has therefore become vitally important to stay one step ahead of the threats that grow every day," Crosetto said in a statement.

burs-stu/dva