SENIOR Conservatives want to “maximise” the political pain for Labour on Trident in the run-in to the Holyrood elections.

David Cameron is coming under pressure to opt for a main Westminster vote in March, two months before the May 5 poll, party sources have confirmed.

It is understood that the Scottish Tory leadership is relaxed about whether or not the so-called “main-gate vote” takes place in March or in October.

One senior source stressed the Prime Minister had yet to make a decision on timing but said: “Ruth Davidson’s preference is for an early vote but this is not a demand. Clearly, one consideration is the impact on Labour and what can give us maximum impact.”

Another Conservative insider stressed that political considerations were "peripheral" and that what was important was the issue of maintaining Britain's defence and pressing ahead with the programme to renew its fleet of Faslane-based nuclear submarines.

The Tory hierarchy is said to be divided on when to call the crunch Commons vote but it is believed Michael Fallon, the Defence Secretary, is pushing for it to take place before the Easter recess, which begins on March 24.

Mr Cameron is faced with a happy political dilemma.

A vote in March would expose Labour splits in the run-in to the Holyrood poll when the Scottish Conservatives believe they have their best chance of ousting Labour as Scotland’s second party.

A spring vote would also mean that Labour’s internal review on Trident would be pre-empted. Opposition sources have already made clear that in such circumstances Jeremy Corbyn as leader would have the ultimate say on party policy in consultation with his shadow cabinet.

It is difficult to see the anti-Trident Labour leader proposing a policy with which he personally disagrees.

Equally, several of his colleagues have already signalled that they would resign their frontbench posts if the party’s current UK policy – to support retention and renewal – were changed. Scottish Labour has already voted to abolish the deterrent; a policy opposed by its leader Kezia Dugdale.

If the Trident issue is brought before MPs in March, Mr Corbyn might again have to resort to offering a free vote but this will open up the Labour leadership to the charge of being in complete disarray on the key policy of Britain’s defence.

Meantime, if the Prime Minister delayed a Commons vote until October, then it would happen after Labour’s conference, which would be dominated by its post-review vote on Trident; again exposing splits and potentially sparking frontbench resignations.

The week after Labour’s conference is the Conservative conference. This would take place on a political high following the Opposition’s public display of division on the nuclear deterrent.

A Commons vote when Westminster returns in early October would also see ex-Labour shadow ministers going into the Westminster lobbies with their Tory opponents to support the renewal of Trident.

The SNP, united in its opposition to the nuclear deterrent, would also benefit politically from Labour’s splits but one Conservative source noted how in the Holyrood poll the Scottish Tories’ main target was to increase their number of seats and displace Labour as the main opposition.