A Scottish deficit of almost £15 billion, proportionately more than double the UK’s, places a huge question-mark over the SNP's core mission of independence for Scotland, Jeremy Corbyn has said.

In a speech ahead of tonight’s head to head hustings in Glasgow with challenger Owen Smith, the Labour leader also fired off a barb at Kezia Dugdale, the Scottish Labour leader, who is backing the Welsh MP for the leadership, by suggesting that by not supporting him she was not in favour of an unashamedly anti-austerity programme.

As tension mounts between the two candidates before their showdown in the Scottish Exhibition and Conference Centre, Mr Corbyn in his address referred directly to the Government Expenditure and Revenue Scotland[GERS] statistics published on Wednesday, which showed, due mainly to the 97 per cent fall off in oil revenues, Scotland’s annual deficit had grown to £14.8bn or 9.5 per cent; more than double the UK’s four per cent.

The Labour leader said: “The SNP have a different purpose which is to achieve independence. I respect their right to advance their cause but I also reserve the right to disagree with them and judge, just as a majority of people in Scotland did in 2014, that it would not be in the interests of the people of Scotland.

"Yesterday's GERS figures underline that concern. A Scottish deficit of £15 billion raises a huge question mark over the central economic mission of the SNP.

"A Labour government will demonstrate to the Scottish people that it is Labour which has the answers to the deep unfairness and inequalities that currently stain our country."

Mr Corbyn also took a swipe at Ms Dugdale and her choice to back his opponent, saying: "I stand just as Scottish Labour did in May on an unashamedly anti-austerity platform with policies that will ensure that no-one across Scotland and the rest of the country is left behind.

"I'm therefore disappointed that my friend Kezia Dugdale does not sign up to this programme at the moment."

Earlier, the Labour leader confirmed his decision, revealed by The Herald on Monday, that he would not form an anti-Conservative alliance with Nicola Sturgeon, branding the SNP unreliable.

Earlier this month, Dave Anderson, the shadow Scottish secretary, urged Labour to consider an SNP coalition "if that is the price that we have to pay to prevent another rabid right-wing Tory government".

But in an article for the Daily Record, Mr Corbyn wrote: "Let me make it clear. I will welcome support for all or any of our policies from any other political groups or parties...but I'm well aware that Labour and the SNP come from different traditions and have different goals.

"I don't see a party that welcomed George Osborne's corporation tax cuts, relentlessly attacked local government and is committed to a benefit cap as reliable allies for a radical Labour government.

"There are many people who have voted for, or even joined, the SNP who want to see many of the changes we want to implement. I don't think these people are always being served properly by the SNP."

Meantime, Mr Smith, in an interview with the New Statesman magazine, fired off another criticism at his colleague, claiming Mr Corbyn was more interested in being leader of the Labour Party than Prime Minister of the United Kingdom.

Stressing how he was “deeply worried” the MP for Islington would try to stay on as leader even if Labour lost the next general election under his leadership, Mr Smith said: “He’s determined to hang on come hell or high water. And what does that say about him?...

“He is actually prepared to sacrifice unity and victory – two great words that have traditionally been emblazoned on Labour banners through the ages – in order to secure control of the party,” the Pontypridd MP added.

In a separate development, disgruntled Labour MPs accused Mr Corbyn of failing to work hard enough to protect workers' jobs and of undermining a major campaign event.

Senior backbenchers, including former shadow cabinet ministers Lilian Greenwood and Gloria De Piero, vented their frustration about their leader in a video message in which they pledged their support for Mr Smith.

Anna Turley, who represents the Redcar seat hit by the closure of a steelworks, claimed Mr Corbyn turned up at a protest march but failed to do the hard work behind the scenes to help the industry's workers.

Former shadow transport secretary Ms Greenwood said her leader launched a reshuffle on the day of a campaign against rail fare increases, undermining the hard work done by her team.

Ms De Piero said Mr Corbyn was unable to reach ex-Labour voters who had switched to the Tories in former industrial areas.

Ms Turley said: "I tell you what sums up Jeremy Corbyn for me was when we had a march of the steelworkers in Westminster, he was there at the front, holding the banner.

"But when the hard work needed to be done, when we were meeting with businesses, when we were meeting with industry, when we were meeting with government to try and find the solutions, he wasn't there."

She added: "We need a leader that will roll up their sleeves, that will grab a crisis, and really, really try and fix it. Jeremy Corbyn just is not that leader."

Ms Greenwood expressed her frustration that a campaign tied in with the rise in rail fares was overshadowed by Mr Corbyn's reshuffle in January.

"I was so disappointed, when we had got activists up and down the country, out campaigning on that issue and the same day Jeremy chose to launch his shadow cabinet reshuffle, completely knocking it off the agenda," she said.

"He says, now, that I should have known he was going to do that but it's an absolute nonsense when we had planned that campaign day for weeks.

"It really undermined me and all the hard work that my staff, and our Labour activists up and down the country, had been doing."

Former shadow young people and voter registration minister Ms De Piero, said former coal mining areas near her Ashfield seat in Nottinghamshire had turned Tory.

"We need a leader that can go and listen to those people - not just who did vote Labour but those people who we lost last time who used to vote Labour," she said.

"I don't think Jeremy can reach out."

Former shadow Welsh secretary Nia Griffith insisted that the ex-members of Mr Corbyn's team had tried to make things work before the mass resignations which triggered the leadership battle.

"It's really important that Labour Party members understand that we in the shadow cabinet really wanted to make things work and that we wanted to be loyal as well," she said.