Rachel Reeves must break her fiscal rules to boost defence spending or risk a showdown with Donald Trump, a military chief has warned.

The Chancellor has been urged to make a “special case” for a cash injection for the military, even if it means borrowing more to fund it.

Last month, the president-elect’s team reportedly told European officials they would be expected to increase military budgets to five per cent of GDP after he took office.

This is more than double the UK’s current target, with Labour saying it aims to reach 2.5 per cent but with no timeline set for when this will be achieved.

Admiral Lord West, the former First Sea Lord who was a security adviser to former prime minister Gordon Brown, said: “Everybody who knows anything about defence and the UK military realises that they have been underfunded over a number of years, they are hollowed out and in desperate need of a serious injection of funds.