The RAF could be forced to wait until 2040 to receive Britain's next generation of Tempest fighter jets with funding now expected to be released only towards the mid-2030s rather than the originally planned 2025 development start date.
The advanced jets, designed to replace the RAF's ageing Typhoon fleet, are now unlikely to become operational until the late 2030s or potentially the 2040s.
The new dates mark a substantial setback from initial plans, which envisaged the upgraded aircraft entering service by 2035.
The delays stem from the long-awaited defence investment plan (DIP), which is expected to confirm financial backing for the project will not materialise until several years later than anticipated.
Ministers had previously pledged to deliver a modernised Royal Air Force by 2035.
Shadow Defence Secretary James Cartlidge warned the delay could pose a risk to Britain's defence.
"With the threats we face and war on two fronts, Labour needs to be accelerating programmes that will make us safer, not deliberately delaying them for years," Mr Cartlidge said.
He warned that further postponements to the Typhoon replacement scheme "could be dire" for the RAF and Britain's closest allies.
The RAF's ageing Typhoon fleet is unlikely to be replaced until the late 2030s or potentially the 2040s
|BAE SYSTEMS
Mr Cartlidge accused Sir Keir Starmer of being prepared to sideline the next-generation fighter programme, even at the cost of damaging allied relationships and national defence capabilities.
"This news suggests Starmer is willing to kick our next generation fighter programme into the long grass, even if this damages our allies and our own ability to defend ourselves," Mr Cartlidge said.
"This can only mean one thing: Labour have once again bottled taking the tough decisions to fund defence, and are effectively cutting capabilities to find cash when they should be cutting welfare."
The UK currently operates more than 100 Typhoons, which are scheduled for retirement by 2040.
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Artist's impression of new Tempest fighter jet
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Its replacement, the Tempest programme, is a collaborative venture between Britain, Japan and Italy under the global combat air programme, with costs exceeding £12billion.
An interim development contract worth £686million was agreed between the three nations in April, though this arrangement expires next month.
Uncertainty surrounding the defence investment plan has stalled progress on securing a longer-term agreement for the project.
The Prime Minister is currently considering increased borrowing to fund approximately £18billion in additional defence spending, with other options including significant Whitehall cuts.
The current fleet is set to be retired in 2040
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Defence Secretary John Healey is expected to unveil the defence investment plan next month, with officials treating the Nato summit on July 7 as a firm deadline for publication.
The plan is understood to prioritise drones and autonomous systems, reflecting lessons from conflicts in Ukraine and Iran.
An MoD spokesman said: "The UK remains committed to the global combat air programme, working closely with our international partners to deliver a next-generation combat air capability."
The spokesman added that work continues with Italy and Japan on finalising the full international contract.