In a speech on Saturday at the summit, the UK prime minister will argue that the continent must shift from overdependence on the United States towards a more European NATO.

"I'm talking about a vision of European security and greater European autonomy that does not herald US withdrawal but answers the call for more burden sharing in full and remakes the ties that have served us so well," Starmer is expected to say.

The gathering comes as European leaders remain concerned that a United States led by President Donald Trump can no longer be relied upon to be the guarantor of their security.

Since returning to the White House last year, Trump has frequently criticised European countries for not sharing enough of the burden on common defence, and raised questions about the future of NATO.

European members of the transatlantic military alliance are rushing to build up their defences in the face of an increasingly belligerent Moscow, whose war in Ukraine is set to enter its fifth year this month.

"As I see it -- Europe is a sleeping giant. Our economies dwarf Russia's, 10 times over," Starmer will tell allies, according to excerpts released ahead of his address.

"We have huge defence capabilities. Yet, too often, all of this has added up to less than the sum of its parts," he was to say, citing fragmented planning and procurement problems.

Late last year, talks on Britain joining the bloc's new 150-billion-euro (pound130 billion) rearmament fund broke down, reportedly because London baulked at the price for entry.

Downing Street said Starmer would use his speech to call for closer UK-EU defence cooperation.

"There is no British security without Europe, and no European security without Britain. That is the lesson of history -- and it is today's reality too," Starmer was to say.

The UK government announced on Friday that Britain will spend more than pound400 million this financial year on hypersonic and long-range weapons, including through joint projects with France, Germany and Italy.

Starmer, whose centre-left Labour party is being squeezed on opposite ends of the political spectrum by the anti-immigrant Reform UK group and the more leftwing Greens, was to say leaders "must level with the public" about the defence costs they face.

He was due to hit out at "peddlers of easy answers on the extreme left and the extreme right", according to the excerpts.

"The future they offer is one of division and then capitulation. The lamps would go out across Europe once again. But we will not let that happen", Starmer was expected to say.