General Sir David Richards, a former chief of defence staff, said the decision to raise defence spending over the next two years was a sound strategic move, but one that “almost certainly would not” be happening if not for Trump.

“It was going to happen, it’s now been accelerated by Donald Trump’s actions, and all of us, I think, would say not before time,” he told BBC Radio 4’s Today programme.

Praising Healey as a “forward-thinking, strategically-minded person”, he added: “The one thing I’ve learned as a student of military history, but also from my own experience, you’ve got to keep close to America if you want to be genuinely credible in terms of deterring a potential aggressor.

“There is no way that Europe, at the moment, could worry Russia, for example.”

Lord Richards stressed the British Army was currently “very hollowed out indeed” and suggested the “army isn’t big enough” currently for British troops to be part of a rotation of European peacekeeping forces.

Questions have been raised about the Labour government’s U-turn on its manifesto pledge to raise international development funding by 0.2% of GDP, with unease among some Labour MPs about the move.

Asked whether the increase announced on Tuesday is linked to Sir Keir’s visit to the White House, Healey told the Today programme: “President Trump, over the last two weeks, has been very direct in his challenge.

“He’s reinforced the imperative and the importance of Britain making this commitment and helping other European countries to step up in a similar way.”

The US has been warning European leaders it wants to see a significant increase in their defence contributions to Nato for at least a decade.

Trump’s rapprochement with Russia’s Vladimir Putin, and the US siding with Russia on a UN resolution on Ukraine, has sent shockwaves through European allies.

Asked whether he believed the UK increasing its defence contribution would bring Trump on side, Healey said: “I’ve never had any doubt that President Trump and the US administration… recognise that the UK is the US’s closest defence and security ally – they’ve challenged us to help lead in Europe.”

He added the PM could now tell Trump: “You are challenging Europe and the UK to step up on European security, on Ukraine, on defence spending, on reinforcing our industrial base.

“We are, and we will step up further.”

Healey also said the UK would still spend £9bn on international aid, including in Gaza, prioritising efforts to “deter conflicts that cause the biggest impact on many of the poorest countries”.