By committing to that level of defence spending, Labour, which is far ahead in opinion polls ahead of an election expected later this year, is matching the intentions of the ruling Conservative party.

Speaking to the i newspaper, Starmer said defence was "the number one issue for any government" in a world where international threats have risen and the situation was "more volatile" than it had been for many years.

"On defence spending, obviously we want to get to 2.5% as soon as resources allow that to happen," he said.

He also committed to Britain's nuclear deterrent, the Trident-submarine based missile system which has a continuous at sea presence at a cost of billions of pounds.

"In the face of rising global threats and growing Russian aggression, Labour's commitment to our UK nuclear deterrent is total," Starmer will say later on Friday on a visit to Cumbria, northern England where the submarines are built.

Should Labour win the election, there will be a review of defence and security spending, Starmer told the i newspaper, to make sure the priorities are correct and try to tackle waste in procurement.

Starmer's position is in contrast to Labour's previous leader Jeremy Corbyn, who opposed Britain's Trident nuclear weapons system.

The Conservatives, traditionally seen as the party more likely to spend on defence, promised in March that defence spending would grow to 2.5% of GDP "as soon as economic conditions allow", up from the current level of around 2.2%.

Trident costs about 3 billion pounds per year to run and the cost of the new submarine fleet, set to be operational from the early 2030s, is expected to be 31 billion pounds.

(Reporting by Sarah Young; Editing by Kate Holton)

By Sarah Young