British Prime Minister Keir Starmer will meet his Japanese counterpart Sanae Takaichi on Sunday as uncertainty mounts over their joint fighter jet program with Italy because of doubts about the U.K.’s commitment.

The Global Combat Air Program — an initiative between the three nations to develop a next-generation fighter jet by 2035 — has faced roadblocks including delays to Britain’s financial contribution to the project.

Britain had been expected to unveil billions of pounds for the GCAP in late 2025 as part of its 10-year defense investment plan, but it was postponed by several months due to a spending row between the U.K. defense ministry and Treasury.

That’s left funding for the GCAP and other major U.K. defense programs in limbo.

The investment plan was due to be published in time for Takaichi’s visit and the G7 summit in France, which starts on Monday, but it’s been delayed further after Defense Secretary John Healey stepped down unexpectedly. Healey accused the government of being unwilling and unable to “commit the resources that the nation needs to defend the country at this time of rising threats.”

The U.K. in a statement on Saturday said it remained committed to the program, but failed to say how much money it would invest. Italy’s parliament in February backed a $10.7 billion funding plan for the project, Reuters reported.

Japan has set aside funds for GCAP from its annual budget. Its spending on the project totaled over ¥500 billion ($3.1 billion) in the five years to March, and the government earmarked a further ¥170 billion for the current fiscal year starting April.

The U.K. and Japanese leaders will also discuss a new council to foster bilateral industrial cooperation and accelerate the development of each other’s dual-use technologies such as drones and AI, the U.K. said.

Japan and Italy have grown frustrated with the U.K. for dragging its feet on the funding. A Japanese foreign ministry official avoided commenting directly on concerns over whether the U.K. will pay up, saying the Takaichi administration was working closely with both the U.K. and Italy and will continue to do so.

In an opinion letter to the Financial Times published Friday, Takaichi touted the project as an example of international cooperation that spans continents.

“Our accelerating co-operation with the U.K. and Italy on the Global Combat Air Program is a case in point,” she wrote. “Following the review of Japan’s policy guidelines on the transfer of defense equipment and technology earlier this year, it is expected that cooperation aimed at further enhancing interoperability between Japan, the U.K. and Europe will ensue.”

Any delay would be particularly concerning for Japan, which is set to start retiring its F-2…