After growing criticism, the prime minister eventually provided a timeline for the announcement of the long-awaited increase, stating that the UK will "set out a plan" to increase defense spending to 2.5% of national revenue in the spring.

Sir Keir Starmer gave the date during a phone call with Mark Rutte, the secretary general of NATO, in the wake of threats by Moscow to target UK and US military facilities following a decision by London and Washington to let Ukraine fire their missiles inside Russia.

There was no clarity though on when the 2.5% level will be achieved. The UK says it currently spends around 2.3% of GDP on defence.

A spokeswoman for Downing Street said that the two men "began by discussing the situation in Ukraine and reiterated the importance of putting the country in the strongest possible position going into the winter".

They also talked about the deployment of thousands of North Korean soldiers to fight alongside Russia.

"The prime minister underscored the need for all NATO countries to step up in support of our collective defence and updated on the government's progress on the strategic defence review," the spokeswoman said.

"His government would set out the path to 2.5% in the spring."

The defence review will also be published in the spring.

While a date for an announcement on 2.5% will be welcomed by the Ministry of Defence, analysts have long warned that such an increase is still well below the amount that is needed to rebuild the armed forces after decades of decline to meet growing global threats from Russia, an increasingly assertive China, North Korea and Iran.

They say the UK needs to be aiming to hit at least 3% - probably higher.

With Donald Trump returning to the White House, there will be significantly more pressure on the UK and other European NATO allies to accelerate increases in defence spending.