As the Cold War ended and the Soviet Union’s grip on Europe ebbed away, the British Army still had more than 150,000 troops.

Fast forward 36 years and it now has less than half of that, at around 70,000, while the size of the Royal Navy and the Royal Air Force have also fallen dramatically.

The scale of this depletion has come to the fore amid the resurgent threat from Russia, compounded by Donald Trump’s bid to scale back America’s military presence on the Continent.

Sir Keir Starmer has warned that Britain and its allies now face “a generational moment” and cannot “cling to the comforts of the past”.

“It is time to take responsibility for our security,” the Prime Minister said in a speech on Sunday, highlighting the race to rearm across the West.

However, his comments come as the Government faces pressure to spell out how it will boost UK defence spending to 2.5pc of GDP, against a backdrop of Trump demanding Nato members pay as much as 5pc.

So what does Britain need to do to deter Russia? And how might we pay for it?