Military chiefs have warned Sir Keir Starmer that the Government’s defence spending plans “won’t touch the sides”, Whitehall sources have revealed.

Labour has pledged to raise defence spending to 2.5 per cent of GDP, but is yet to set a date to implement the increase.

Donald Trump has called on Nato nations to spend 5 per cent on defence in his effort to force Europe to take on more responsibility for Ukraine.

The Telegraph understands that the Government’s delay in raising defence spending and its refusal to agree to more than 2.5 per cent has led to fears among military chiefs that the Armed Forces will be unable to meet current targets.

“This 2.5 per cent figure won’t touch the sides,” a senior Whitehall source told The Telegraph.

“But the figure depends on what you want the British military to do. The figure could be less, but then we do less.”

They said ambitions for the Armed Forces would have to be reined in unless the Ministry of Defence secures “big, big lumps of money needed for defence over a sustained period of time”.