Italy will join the British-led Team Tempest programme building an advanced fighter jet, boosting the project's chances of getting the aircraft off the ground.
Confirmation of the latest member of the project is expected to come at the giant DSEI military exhibition in London’s Docklands this week.
Tempest is a collaboration between the British Government and industrial partners BAE Systems, Rolls-Royce, MBDA and Leonardo.
It aims to build a “sixth generation” fighter featuring stealth technology, laser weapons and a swarm of drone wingmen which will be in service in 2035.
It will guarantee work for Britain’s £6bn-a-year combat aircraft industry that employs 18,000 people and is a major source of defence exports.
Italy coming on board - joining Sweden, which agreed to work alongside Tempest on future combat in the summer - could be announced as soon as Tuesday. The timing may also be affected by Brexit-related political turmoil in Westminster.
Italian aerospace company Leonardo’s UK business is already involved, but the Rome government signing up is a further boost.
It is not yet known how the agreement - which will be between the UK and Italian governments, rather than industrial companies - will operate.
However, it could be similar to the way in which Sweden joined, with the Stockholm government working with the UK to assess future technologies, with the potential for this to be expanded in the future.
“Italy coming on board is a very positive sign,” said independent defence analyst Howard Wheeldon. “It’s not just because it potentially means more money for R&D and a bigger market for the aircraft.
“It’s a sign of confidence in Tempest - it says ‘this project is happening now’, rather than ‘this is going to happen’.”
Tempest was launched at the Farnborough air show last year, with a £2bn funding commitment from industry and government to kick off research.
However, this is just a fraction of the cost of developing and actually building a new warplane.
From the start the UK government said it would not be able to go it alone and would seek partners to help with funding and increase the total number of aircraft likely to be built.