“What is our Government doing? Has anyone heard from Wes Streeting, the former head of the National Union of Students, who has rocked up as Defence Secretary?”

She added: “We have to stop pretending that we are living in a carefree end of history when Russia is testing our resolve week after week. It’s time to get serious.”

The Leader of the Opposition hit out at Mr Burnham for sending a “dangerous” message that he would not cut welfare to fund the military – a signal she warned was “heard loud and clear in Moscow as well as Manchester.” The Conservatives have intensified their attacks on welfare spending after the Prime Minister recently stated that national security cannot “come at the expense of social security”.

Downing Street insisted Mr Burnham remains committed to both funding the armed forces and bringing down the benefits bill, though not through “crude cuts”.

Former military leaders backed calls for urgent rearmament. Admiral Lord West, the former First Sea Lord and Gordon Brown’s security minister, warned that Britain’s military is in “quite a parlous state.”

“In many ways, one could argue we are already at war. We are certainly in the grey zone – whether it’s cyber attacks, drones getting near the edge of somewhere or threats to underwater cables,” Lord West said.

Former chief of the general staff Lord Dannatt urged Chancellor John Healey to set out a clear path to 3.5% of GDP on defence at the upcoming Budget, adding: “My bottom line is that Andy Burnham, and regretfully I would now add John Healey, are playing fast and loose with the nation’s security”.

While the UK has promised to reach 3.5% of national income for defence by 2035, in line with NATO pledges, the Government’s current budget only raises spending to 2.7% by 2027-28, facing mounting pressure to explain how further targets will be met. Mrs Badenoch has pledged to raise defence spending to 3% of GDP by 2030 by capping housing benefit to raise £4 billion – a proposal the Prime Minister claims would cause unprecedented levels of homelessness. The Tories rejected those claims, suggesting claimants would instead need to “move somewhere cheaper.”

A Foreign Office spokesperson defended the Government’s record, stating: “These threats from Russia are yet another attempt to distract from their barbaric invasion of Ukraine.

“We have been clear that Russia’s hybrid attacks are egregious and unacceptable. That’s why we have taken tough action to respond to Russia’s intensifying hostile activity against our continent – increasing defence spending, expelling intelligence officers, sanctioning the GRU, cracking down on illicit finance networks, and ensuring Russia’s criminal proxies are disrupted and brought to justice.

“The UK is united with our allies on the importance of defending ourselves, and Russia’s aggression will not deter us from supporting Ukraine.”