LABOUR’S internal battle over Trident is set to intensify still further as Len McCluskey, the leader of Unite, is preparing to warn Jeremy Corbyn at his union’s Scottish conference this weekend not to try to fix the policy in his favour.

Mr McCluskey’s broadside is expected to come on Sunday, just 24 hours after the Labour leader is due to address the same event in Glasgow.

Already, Sir Paul Kenny, who leads the GMB union, has fired a warning shot across Mr Corbyn's bows, emphasising how there are tens of thousands of jobs at some 50 UK sites dependent on defence contracts.

"There is a process and there are rules and if anybody thinks that unions like the GMB are going to go quietly into the night while tens of thousands of our members' jobs are literally swannied away by rhetoric, then they have got another shock coming," declared Sir Paul.

A Unite source made clear that Mr McCluskey would echo the sentiments of his union colleague.

"Our policy has been the same since 2010 and it's not likely to change until our own conference in July, if indeed it changes at all,” he declared, stressing: “Put it this way, no one has sought to change it.”

The source told the Politicshome website: "This is the first time we'll have heard from Len this year and it will be interesting to hear what he says to Scottish workers, some of whom will be from the defence and shipbuilding industry."

Last September, both unions joined forces at the Labour party conference to stop the party's Trident policy from being debated.

Mr McCluskey declared at the time: "We won't be voting in favour of any anti-Trident resolution."

The UK conference endorsed the party’s "commitment to a minimum, credible, independent nuclear capability, delivered through a continuous at-sea deterrent".

But weeks later, the Scottish Labour Party voted to oppose Trident renewal.

Earlier this week, Mr Corbyn, who is bitterly opposed to maintaining Britain’s nuclear deterrent, stressed how he wanted “members to have a big say" on policy.

Some Labour MPs believe the leader is seeking to “stitch up” Labour’s defence review after replacing pro-Trident Maria Eagle as shadow defence secretary with anti-Trident Emily Thornberry, who conduct it alongside Corbyn ally Ken Livingstone, who is also opposed to the nuclear deterrent.

But any hope the Labour leader had of easily reversing Labour’s backing for Trident suffered a setback this week when Iain McNicol, the party’s general secretary, made clear the only way policy could be changed would be through the annual conference. Given the power of the unions, Mr Corbyn’s desire for change could well be thwarted.

Meantime, Green Party MP Caroline Lucas has taken over from Mr Corbyn as the chair of Westminster’s cross-party Campaign for Nuclear Disarmament group. He will, however, remain as CND's vice-president but has quit the parliamentary role because of time pressures.