The UK should consider “decisively” increasing defence spending after Brexit, Foreign Secretary Jeremy Hunt has said.
He told the Lord Mayor’s Banquet in London the threats facing the UK had changed “markedly” since the Cold War.
“We simply do not know what the balance of power in the world will be in 25 years’ time”, he added.
He said any extra money should be spent on “new capabilities and not simply plugging gaps”.
Mr Hunt said it was “not sustainable” to expect the US to spend 4% of its GDP on defence while other Nato allies spent between 1% and 2%.
“So for these and other reasons I believe it is time for the next Strategic Defence and Security Review to ask whether, over the coming decade, we should decisively increase the proportion of GDP we devote to defence,” he said.
The foreign secretary is among those expected to stand to succeed Theresa May as leader of the Conservative Party when she steps down.
Pressure has grown on the PM to set out a date for her departure following the Conservatives’ drubbing at the local elections.
Mrs May has already promised to go once the first stage of Brexit is over.
Other contenders include former and current members of the cabinet, including Boris Johnson, Michael Gove, Amber Rudd, Sajid Javid, and Dominic Raab.
Former cabinet minister Esther McVey and International Development Secretary Rory Stewart have already announced that they plan to run.
All Nato members agreed during 2014 to increase their defence spending to 2% of GDP by 2024.
In his speech on Monday, Mr Hunt said the UK currently accounted for almost 20% of total EU defence spending, and British forces contributed a “hugely disproportionate share” of some key capabilities.
But he added that the UK had entered a “multipolar world” without the “assurance provided by unquestioned American dominance”.
“We face a more aggressive Russia and a more assertive China. We simply do not know what the balance of power in the world will be in 25 years time,” he said.
On Brexit Mr Hunt said the UK must leave the EU “cleanly and properly”, and to fail to do so “would betray the promise of a democracy”.