WESTMINSTER'S key vote to approve the £167 billion Trident replacement programme could come before Christmas, senior Whitehall sources have revealed.

The main-gate decision by the UK Government had always been pencilled in for early next year. But David Cameron and his colleagues are keen to try to defuse the issue as much as possible ahead of the May 2016 Holyrood elections.

It is believed that consideration had been given to putting the main-gate decision back until after the Scottish poll in the summer or autumn of 2016. But one senior insider close to the Prime Minister said: "It could come before Christmas or in January. We want to get it out of the way before" the Scottish elections.

Trident is a totemic issue for the SNP. With Labour deeply split under Jeremy Corbyn's leadership, the Tories, gaining ground in opinion polls in Scotland, are the only party pushing heavily for a like-for-like replacement of Britain's nuclear deterrent.

Conservative strategists believe trying to take as much heat out of the issue ahead of the Holyrood campaign will help limit any damage the Tories will face following the controversial Westminster decision to approve a new generation of nuclear submarines based at Faslane.

Trident will hit the headlines again next week when MPs debate and vote on the issue. With Nationalist and Tory positions well-delineated - the SNP has organised the debate - the focus will be on Labour.

Scottish Labour recently voted to oppose replacement, falling into line with Mr Corbyn's own view.

The UK party voted at its autumn conference to support replacement - in line with the view of Scottish Labour leader Kezia Dugdale - but aides to the UK Labour leader have made clear that, now the policy is under review, the UK party has, in effect, no official policy.

Suggestions have been made that Mr Corbyn will order his MPs to abstain in Tuesday's vote. But with the rebellion against the party leader getting more vociferous, a showdown is expected in the Commons, all of which will help the Tories and the SNP highlight how their Labour opponents belong to a deeply divided party.

This was illustrated by the spat between Ken Livingstone, the former London Mayor and left-wing ally of Mr Corbyn, and Kevan Jones, the party's former defence spokesman.

After Mr Jones questioned Mr Livingstone's ability to co-chair the party's Trident review, the left-winger, who opposes the nuclear deterrent, suggested his colleague needed "psychiatric help".

Mr Jones, who has spoken publicly about his past struggle with depression, said the comments belonged in the "dark ages" and demanded an apology.

After Mr Corbyn, who has campaigned to raise the issue of mental health, urged Mr Livingstone to apologise, he did so unreservedly.

But on Channel Four the two politicians continued their public spat.

The former mayor told Mr Jones: "You provoked this row. You questioned my ability to do this job."

His colleague replied: "So that excuses your grossly offensive language?" to which Mr Livingstone replied. "I thought your attack on me was grossly offensive."

Meantime in the Commons, Chris Grayling, the Leader, said scrapping Trident would turn an important part of Scotland into a "wasteland".

The Cabinet Minister said deciding not to renew Britain's nuclear submarines would harm the area around their base at Faslane, on the banks of the Clyde, because thousands of jobs would be lost.

Unions have warned that around 13,000 could go if Trident is scrapped.

Mr Grayling was later forced to clarify his comments after Labour's Ian Mearns said: "The area around Faslane, with or without Trident, I don't think could ever be described as being a wasteland, it's beautiful countryside."

The Commons leader replied: "There was never any doubt about the beauty of the countryside in western Scotland and indeed in Scotland as a whole, it is a fantastic part of this country and something that we all wish to spend time in."