Japan’s patience with Britain as a defence partner is being tested after reports that funding shortfalls in London could delay a next-generation fighter jet that both countries are developing with Italy.

The Global Combat Air Programme, or GCAP, is intended to deliver a new fighter for the three countries by 2035, but The Telegraph reported on Saturday that the aircraft could be delayed by several years because of uncertainty over Britain’s defence spending plans.

The report has raised concerns that Japan may have to extend the service life of fighters that GCAP was meant to replace, potentially weakening national security amid growing pressure from China’s expanding air power.

“My contacts in the defence and security community here in Tokyo are expressing a high degree of frustration and disappointment in the British approach,” said Garren Mulloy, a professor of international relations at Daito Bunka University and a specialist in military issues.

The Telegraph reported that Britain’s Defence Investment Plan, intended to outline upgrades across its armed forces, had been delayed after initially being expected last autumn.

According to the report, the plan is expected to confirm that funding for GCAP will be released only in the mid-2030s because of the state of Britain’s national finances, and that the aircraft may not be deployed until the early part of the following decade.