ROME — Japan, Italy and the U.K. have handed a £4.6 billion ($6.1 billion) development contract to their national champions building the GCAP jet, days after the U.K. freed up crucial cash to make it happen following a months long hold-up.

The three nations said on Friday they had handed the 18-month contract to Edgewing, the industrial consortium grouping firms building the sixth-generation fighter.

The announcement came three days after the announcement of the U.K.’s delayed Defence Investment Plan (DIP), which contained funds for the fighter.

“The £4.6 billion contract will enable completion of the advanced concept and assessment phase of the program, and further joint detailed design and development,” the tri-nation agency running the program announced.

As the partners awaited the publication of the DIP this spring, they handed firms a £686 million stop-gap contract to keep work going until June 30.

To the relief of the partner firms, the DIP – which was released on the same day the stop gap contract expired – committed £8.6 billion ($11.4 billion) over four years to the program, more than the £6 billion expected.

The U.K.’s delay in finding the GCAP money sparked criticism from Japan, which is anxious to get a sixth-generation jet flying by the planned GCAP delivery date of 2035.

Japan’s prime minister reportedly threatened to pull out of a planned visit to the U.K. before the G7 in June if the U.K. failed to promise funding.

The signing of the contract comes days ahead of the opening of the U.K. Farnborough airshow this month.

U.K. defense procurement minister Luke Pollard called the contract “a major step forward towards delivery” of the GCAP.

He added, “This milestone strengthens our partnership with international allies, supports thousands of highly skilled jobs across the UK, and will give the RAF the tools they need to keep the UK safe, all backed by an £8.6 billion commitment in the defense investment plan.”

Edgewing, the industrial consortium running the program teams local champions BAE Systems, Leonardo, and Japan Aircraft Industrial Enhancement Co. Ltd. (JAIEC).

Edgewing is now expected to hand its own contracts to tri-nation consortia managing the electronics and propulsion on the jet.