WARSAW (AFP) - British Prime Minister David Cameron said on Saturday (July 9) that parliament would vote on July 18 on the renewal of the country's Trident nuclear weapons programme.

"Today I can announce that we will hold a parliamentary vote on the 18th of July to confirm (lawmakers') support for the renewal of a full fleet of four nuclear submarines capable of providing around-the-clock cover," Cameron said at a Nato summit in Warsaw.

"The nuclear deterrent remains essential in my view not just to Britain's security but as our allies acknowledge here today to the overall security of the Nato alliance," he told a press conference.

Conservative leader Cameron, who is to step down by September after Britain voted to leave the European Union, has previously committed to a £20 billion (S$34.9 billion) plan to maintain the submarine-based system.

The leader of the main opposition Labour party Jeremy Corbyn has opposed the upgrade but a significant part of his increasingly rebellious MPs are likely to back it.

The future of Britain's nuclear deterrent is however in question as the submarines are based in Scotland, where the government is considering a second independence referendum following the Brexit vote.

Asked why he was pushing through the vote before handing over to his as-yet-undecided successor, Cameron said it was a pledge in his party's 2015 election manifesto "and we need to get on with that." "I don't think it needs to be caught up in the leadership contest (of the Conservative party) and we will be doing it on the 18th of July," he said.

"It makes sense to hold this vote now, for it to go ahead so our military planners can get on the investment that is needed."