LABOUR’S deep divisions over Britain’s nuclear deterrent are being laid bare today as all but one of Scotland’s 59 MPs are set to vote against replacing Trident.

Jeremy Corbyn has been warned that he faces a backlash from trades unionists if, as expected, he tonight votes in a landmark Commons vote against replacing the four Clyde-based Vanguard submarines, which carry the Trident nuclear missiles.

The Labour leader, a long-standing member of CND, made clear last September when he won the party crown that there were no circumstances in which he would push the nuclear button. Scottish Labour has also come out against retaining and renewing the nuclear deterrent.

Tim Roache, the head of the GMB union, insisted the Labour leader should abide by existing party policy, which is to back Trident renewal. He warned that 45,000 jobs around the country - many of them highly skilled - were dependent on the programme going ahead.

Mr Roache, who supported Mr Corbyn as leader, said: "The Labour Party have a clear policy. The clear policy is that Labour will uphold an at-sea deterrent.

"I would expect, therefore, all Labour MPs, including the leader of the Labour Party - in fact, especially the leader of the Labour Party - to uphold that current policy," he declared.

With Mr Corbyn set to face a leadership challenge from either Angela Eagle or Owen Smith, Mr Roache said he would now be balloting his 640,000 members on whether or not they believed he was still the right person to lead the party.

His comments came as Tom Watson, the deputy Labour leader, warned of "consequences" for trade union bosses, such as Unite general secretary Len McCluskey, who continued to back Mr Corbyn.

"You have Len McCluskey strongly supporting Jeremy Corbyn, who will be voting against the Trident programme tonight, which will put many defence workers in Unite out of their jobs if he gets his way.

"If I was a defence worker in Unite and I was reading social media that Unite were about to give Jeremy Corbyn a quarter of a million pounds of my subscriptions, I would be furious," said Mr Watson.

While the Midlands MP said he expected the "vast majority" of Labour’s 230 MPs to support the UK Government motion backing Trident replacement, he acknowledged that the continuing divisions were harming the party.

"It is not a great position for the Labour Party to be in, to be honest. It doesn't show clarity of thinking, nor do I think it would reassure people that we are strong enough on security matters.

"We might know that this is political skulduggery by the Tories but the country expects us to know our position on strategic defence matters, particularly something so important as our independent nuclear deterrent."

Mr Watson added that while the Trident vote was a political fix, which was causing difficulty for Labour “nevertheless, you have to take a position if a vote of this magnitude is put at Westminster; to abstain is to not take responsibility”.

But abstaining is precisely what his colleagues, Emily Thornberry, the shadow foreign secretary, and Clive Lewis, the shadow defence secretary, have pledged to do.

They have insisted the Commons vote is irrelevant and accused the Conservative Government of "playing games" to embarrass Labour.

Ms Thornberry, who is leading a review of Labour defence policy, said Mr Corbyn would always support unilateral nuclear disarmament regardless of the outcome but that they were looking at a "range of options" in relation to the future of the deterrent.

She told BBC Radio 4's Today programme: "Jeremy is going to campaign and always will campaign for unilateral disarmament. That has always been his position.

"The Labour Party has to come to a collective decision and we have to do that by way of collecting evidence and considering it in a proper way."

With Labour effectively split three ways, the vote is expected to result in a comfortable victory for the UK Government.

Theresa May, making her first appearance at the Commons despatch box since becoming Prime Minister, will use the debate to warn that giving up the deterrent would be a "reckless gamble" with Britain's national security.

She will tell MPs the nuclear threat "has not gone away", and if Britain gives up its deterrent it will be "almost impossible" to get it back.

She will say: "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."