Parliament will vote on plans to upgrade the nuclear Trident fleet on July 18, David Cameron has announced at a NATO summit in Poland.

"We must also invest in the ultimate insurance policy of all, our nuclear deterrent," he told a press conference as he discussed the UK's defence spending commitments.

So today I can announce that we'll hold a parliamentary vote on the 18 of July to confirm members of parliaments' support for the renewal of a full fleet of four nuclear submarines capable of providing around-the-clock cover. The nuclear deterrent remains essential in my view, not just to Britain's security, but as our allies have acknowledged her today, to the overall security of the NATO alliance. David Cameron

The renewal of Trident has proved controversial. The Labour leader Jeremy Corbyn does not support the renewal of the nuclear fleet though other members pf his party do back the upgrade.

A renewal will cost billions and some argue it is a waste for a deadly weapon that is unlikely to be used. Others say its existence a vital deterrent against attack.

Mr Cameron defended his decision to call the vote himself instead of leaving it to a successor who will be appointed within months.

He said he wanted to hold the vote to put the renewal "beyond doubt" so military leaders could begin planning and spending decisions could be taken.