Rishi Sunak has challenged the UK’s European allies to meet his £75bn pledge to increase defence spending as President Biden signed a $61billion package of aid for war-torn Ukraine.
The prime minister warned the world was now “more dangerous now than at any moment since the Cold War” as it faces what he has called "an axis of authoritarian states".
He also defended what he said were entirely "entirely reasonable” calls from his US counterparts for greater European defence spending.
His words will be seen as a message to Donald Trump not to quit Nato should he win the keys to the White House later this year.
Mr Trump has previously said the US would remain in the defence alliance as long as European countries "play fair" and do not "take advantage" of support from America, which spends more on defence.
But the defence secretary Grant Shapps risked sparking a diplomatic incident over the months-long political wrangling that delayed the US aid package for Ukraine.
He said it reminded him of “the old maxim of Winston Churchill, that the United States can always be relied on to do the right thing, once they have exhausted all other options”.
Announcing that the US will send fresh weapons and equipment to Ukraine “right away”, Mr Biden said money would “make the world safer”. “It’s a good day for America, a good day for Ukraine and a good day for world peace. [The aid package is] going to make America safer. It’s going to make the world safer. And it continues America’s leadership in the world.”
He conceded that it had been a “difficult path... but in the end, we did what America always does: We rose to the moment, came together. We got it done.”
Mr Sunak will use a summit to mark the 75th anniversary of Nato in Washington DC in July to lobby allies to match his defence spending commitment, Mr Shapps said.
Both men are set to argue that spending 2.5 per cent of gross domestic product (GDP) should be the benchmark for members of the alliance.
Mr Shapps said: "We're now saying we think that should be 2.5%. We think in a more dangerous world that would make sense.”
He told Sky News: "I will be arguing that, and I know that the Prime Minister feels strongly about it, when we go to the Nato 75th anniversary summit which is in Washington DC."
The previous target of 2 per cent target was set 10 years ago "when we didn't have the significant rise of China, North Korea now nuclear-armed, Iran attacking and using its proxies to attack, and a very much less stable world given Russia's full-scale invasion of Ukraine", Mr Shapps added.
At a press conference alongside German chancellor Olaf Scholz, Mr Sunak said he was “making a choice to prioritise defence”.
He said it was the “right thing to do because whether we like it or not the world is more dangerous now than at any moment since the Cold War and it falls on leaders... to do what’s necessary to keep our continent safe and stand up for our values."
Mr Sunak also said it was “not new” for US presidents to call for more European defence spending, which he said was “entirely reasonable”.
He warned: “We cannot expect Americans to pay any price, to take any burden if we in Europe are not ourselves prepared to make those sacrifices and make those investments.”
Pressed to rule out cuts to public services to fund the change, the prime minister said: "We have record investment in our public services, including the NHS - that’s not going to change, it’s going to continue.
"We have record investment in our schools - that’s not going to change, it’s going to continue to increase.”
The prime minister even claimed it was possible to press ahead with the plans and “cut people’s taxes”.
Mr Sunak’s announcement comes as he furiously tries to close the polling gap with Labour ahead of a general election this year.
In a speech last Friday he pledged to end Britain’s “sick note culture”, while on Monday he held a No 10 press conference to set out details of Rwanda deportation plan.
On Tuesday, Mr Sunak pledged to reach 2.5 per cent by 2030, which the government said would spend more than £75 billion more on defence over the next six years compared with current levels.
It will be paid for in part by slashing 72,000 civil service jobs but he is under fresh pressure to explain where the money is coming from, with a top economist describing claims it is “fully funded” as “a joke”.
Labour has called on the prime minister to explain how the promise will be funded.
Shadow attorney general Emily Thornberry said Mr Sunak had “essentially committed to spending another £75bn on defence by 2030” without “a single line of detail on where their money was coming from”.
And Torsten Bell, chief executive of the Resolution Foundation think tank, said the government’s explanation of how the pledge will be funded is “a joke”.
Mr Bell said raising defence spending to 2.5 per cent of GDP would require even deeper cuts to other departments than those already pencilled in.
Economists last month warned that chancellor Jeremy Hunt’s national insurance giveaways were dependent on “big implicit cuts in public investment spending overall” after the next general election.
At the time, Institute for Fiscal Studies (IFS) director Paul Johnson said spending on services outside of health, defence and education will have to fall by around £20bn under the government’s plans.
And, responding to the government’s announcement, IFS economist Ben Zaranko accused ministers of basing the spending pledge on “dodgy baselines”.
Mr Zaranko noted that the figures used to calculate the extra £75bn spending promised was based on the alternative being a defence spending freeze until 2030.
He pointed out that the actual extra spending pledged amounts to £20bn over the next six years.
And he said: “The government is trying to have it both ways by saying this is a game changing amount of investment going into defence, but also this is small enough that we can make up for it by getting rid of a few thousand civil servants.”
Mr Sunak has said the pledge will be paid for by reducing the civil service back to pre-pandemic levels, as announced by Mr Hunt last October.
The government says this will raise an extra £2.9bn per year to fund the defence spending, but when Mr Hunt originally announced the plans he said they would only raise up to £1bn.
A spokesman for Mr Sunak on Wednesday could not say why the move would now save almost three times as much.
