THERESA May will today claim that scrapping Trident would be a "reckless gamble" likely to embolden the UK's enemies ahead of a key vote on renewal of the nuclear deterrent.

The Prime Minister, in her first Commons statement since replacing David Cameron, will attack the "misplaced idealism" of those who would abandon what she described as the "ultimate safeguard". A Government motion in favour of commissioning four new nuclear-armed submarines is expected to win support of a majority of MPs tonight.

The vote is likely to expose bitter divisions within Labour, with under-fire leader Jeremy Corbyn expected to oppose the motion but more than half of his MPs predicted to offer backing to the Government.

Read more: Trident challenge for Theresa May as support for renewal falls

Labour's shadow foreign and defence secretaries yesterday issuing a desperate call for abstentions, claiming the vote had been orchestrated by the Tories solely to "sow further divisions" within the opposition.

Tom Watson, the party's deputy leader, rejected the call, saying there is a "duty to take a position" while leadership challenger Owen Smith said he would back renewal, with Labour MPs to be offered a free vote.

HeraldScotland: A Trident Ii, Or D-5 Missile, being launched

Ms May, who will open the debate, will warn that "the nuclear threat has not gone away, if anything, it has increased". She is expected to add: "It is impossible to say for certain that no extreme threats will emerge in the next 30 or 40 years to threaten our security and way of life. And it would be a gross irresponsibility to lose the ability to meet such threats by discarding the ultimate insurance against those risks in the future.

"Once nuclear weapons have been given up it is almost impossible to get them back – and the process of creating a new deterrent may take decades.

Read more: Trident challenge for Theresa May as support for renewal falls

"We cannot compromise on our national security. We cannot outsource the grave responsibility we shoulder for keeping our people safe. And we cannot abandon our ultimate safeguard out of misplaced idealism. That would be a reckless gamble: a gamble that would enfeeble our allies and embolden our enemies. A gamble with the safety and security of families in Britain that we must never be prepared to take."

The SNP's 54 MPs will vote against Trident renewal, Nicola Sturgeon confirmed, as she launched an attack on the timing of the vote. The First Minister said: "We are in a period of huge uncertainty where the principal party of opposition is in chaos, the party of Government has been in chaos for the last few weeks. There hasn't been the opportunity to focus properly on the massive issues that are involved with a decision about Trident.

"It's wrong to have this decision as a way of playing games with the chaos in the opposition, which is what I think the Tories are trying to do."