Sir Keir Starmer announced that foreign aid would be cut to boost defence spending.

The Prime Minister said the amount spent on defence would go up from 2.3% to 2.5% of gross domestic product in 2027.

The increase, which comes amid pressure from Donald Trump and Russia’s invasion of Ukraine, will be funded by slashing overseas aid from 0.5% of gross national income to 0.3%.

Speaking in the House of Commons this afternoon, Sir Keir said the plan amounted to “the biggest sustained increase in defence spending since the end of the Cold War”.

He said: “We must change our national security posture, because a generational challenge requires a generational response.

“That will demand some extremely difficult and painful choices.

“And through those choices, as hard as they are, we must also seek unity, a whole society effort that will reach in to the lives, industries and the homes of the British people.”

The change will mean spending £13.4 billion more for defence every year from 2027.

Sir Keir added that he wanted the figure to reach 3% of gross domestic product during the next parliament.

Taking spending on the security and intelligence services into account as well as defence, the budget will amount to a 2.6% share of the economy from 2027.

The PM will travel to Washington later this week for talks with the US President, who has repeatedly pushed for Europe to increase its defence spending.

Setting out the need for the UK to respond, the Prime Minister told MPs: “One of the great lessons of our history is that instability in Europe will always wash up on our shores and that tyrants like (Vladimir) Putin only respond to strength.”