Britain's outgoing prime minister David Cameron said on Saturday he would hold a parliamentary vote on July 18 to decide on the renewal of Britain's nuclear deterrent, in an apparent move to underscore London's commitment to European security.

The replacement of Trident, which was backed in principle by parliament in 2007, has raised questions about national security as Britain's vote to leave the European Union fuels doubts about its future status on the world stage.

The Conservative government says the nuclear deterrent is vital to keep Britain safe in an increasingly hostile world, but some opposition figures say it is indefensible to spend billions on renewing the programme at a time of austerity cuts.

"Today I can announce that we'll hold a parliamentary vote on July 18 to confirm members of parliaments' support for the renewal of a full fleet of four nuclear submarines capable of providing around-the-clock cover," Cameron told a news conference at the NATO summit in Warsaw.

"The nuclear deterrent remains essential in my view, not just to Britain's security, but as our allies have acknowledged here today, to the overall security of the NATO alliance."

The government has indicated the price tag for replacing the fleet has risen since 2007 but has not given a full cost over its expected 30-year life. Calculations by Reuters and a Conservative lawmaker suggest it could reach 167 billion pounds.

Cameron, who resigned after last month's EU referendum and is due to be replaced as prime minister by early September, said replacement of the ageing fleet of four submarines carrying nuclear weapons needed to be put "beyond doubt".-Reuters