More than 1,000 Labour councillors have backed Owen Smith as their next leader citing the chance of another independence referendum.

The group claim that the UK faces an ‘existential threat from nationalists and poor-bashing Tories’ in the wake of the shock vote to leave the European Union.

The warning comes as the Labour leadership race continues to divide the party.

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Both Mr Smith and current leader Jeremy Corbyn will be in Glasgow next week for the latest in a series of elections hustings.

They are expected to face questions about the SNP, after Mr Corbyn’s shadow Scottish Secretary Dave Anderson prompted fury within Scottish Labour by suggesting that the parties could form an alliance at Westminster.

In a letter the councillors, from Scotland, England and Wales, write that they do not have faith in Mr Corbyn’s “weak leadership”.

“The stakes couldn’t be higher," they say.

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"Our country faces an existential threat from nationalists and poor-bashing Tories. A new Scottish referendum is on the horizon. This is no time for Labour to keep fighting itself. The next general election has already begun. Owen Smith, with his experience, especially as Shadow Secretary of State fighting austerity, has a firm grasp of the issues and will be prepared to lead our party from day one.”

They also warn that militants in both wings of the party are “determined to carry out a civil war against each other”.

Earlier a Labour peer and former head of the Royal Navy hit out at Mr Corbyn over Nato.

Lord West accused his party leader of showing a "complete lack of understanding" of the role of the nuclear alliance.

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During a hustings on Thursday night, Mr Corbyn repeatedly refused to say if he would send British troops to help defend a Nato ally if he became Prime Minister.

He said: “I would want to avoid us getting involved militarily by building up the diplomatic relationships and not isolate any country in Europe."

He added: “I don't wish to go to war, what I want to do is achieve a world where we don't need to go to war, where there is no need for it - that can be done.”

Mr Smith, meanwhile, said that he would intervene to protect a Nato country.

Lord West said that Mr Corbyn’s comments showed a “complete lack of understanding of what Nato is, just as he doesn't understand the concept of having a nuclear deterrent. We belong to an alliance, but he stood up and told our allies 'I'm not necessarily sure that we'll come to help you'. I find it quite extraordinary that he's saying that.

"He's stating platitudes because it gets the unthinking masses to vote for him. He should not lead the nation because it leads to war when you don't stand up to bullies,” he told the PoliticsHome website.

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Meanwhile, Paul Sinclair, a former adviser to Gordon Brown and ex-Scottish Labour leader Johann Lamont, attacked what he described as the ”desperately self-indulgent” team surrounding Mr Corbyn.

“I fear they may be destroying the Labour Party,” he said, “and I think that’s bad for everybody in our entire democracy.

“It’s just self-indulgent, student – late middle-aged, sometimes elderly – student self-indulgence that is running Jeremy Corbyn’s party and I don’t think they speak for anybody.”

A former member of Mr Corbyn’s frontbench Heidi Alexander described the shadow cabinet shoddy and unprofessional, as she set out her reasons for quitting.

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Mr Corbyn is considered the frontrunner after his landslide election victory only a year ago.

Aides insist that his views on issues like Trident, which place him in conflict with many of his own MPs, are incredibly popular among members and activists.

The winner of the Labour leadership contest will be announced on 24 September.