“If Putin’s incursion into Ukraine has shown us anything, it is that our adversaries such as Russia have a modern capability that we cannot match,” he warned.

Lord West, the former first sea lord, said not only did more need to be spent on defence, but added it was “ridiculous” that the Government was cutting 10,000 troops. 

He said: “We should reverse cuts in the Army, speed up the build rates of the frigates we are supposed to be building and we should be looking at a minimum of 3 per cent of GDP for defence.”

Their pleas were echoed by senior Tory MPs, many of whom also want the Government to increase defence spending from its current level of 2.2 per cent of GDP to at least 3 per cent.

Sir Iain Duncan Smith, the former Tory leader, urged the Government to “review the troop cuts again in light of Russian aggression”. 

“We should ask is now the right time to do this, or should we focus on the direct threat?,” he said. “We have to be very careful that cutting troops does not send the wrong message.”

Tom Tugendhat, chairman of the foreign affairs select committee, said: “Our Armed Forces are the smallest in decades. Our Army is at its smallest in 200 years. This is no time to cut back.”

Tobias Ellwood, chairman of the defence select committee, warned that the world was “moving into a new era of instability, for which Russian aggression forms just one part.

“It’s absolutely right that not just Britain, but all Nato countries, increase defence spending,” he said.

Lord Dannatt added: “As the leading military member within Nato this is just not acceptable. Our allies like Americans are shaking their heads in disbelief at our lack of investment and our adversaries are smiling to themselves.”