JEREMY Corbyn's leadership has been savaged by a Labour MP following its u-turn on the fiscal charter as it emerged maintaining a collective line with Scottish Labour on anti-austerity was partly behind the controversial move.

Ahead of a potentially explosive Shadow Cabinet meeting this morning, senior backbencher Mike Gapes wrote on Twitter: "There is now no collective shadow cabinet responsibility in our party, no clarity on economic policy and no credible leadership."

Challenged by another user of the social media site to show loyalty to Mr Corbyn, the Ilford South MP responded: "I will show loyalty in the same way as he was loyal to Kinnock, Smith, Blair, Brown, Beckett, Miliband and Harman. Ok?" Mr Corbyn famously rebelled more than 500 times from the backbenches.

During a stormy meeting of the Parliamentary Labour Party on Monday night, John McDonnell, the Shadow Chancellor, sought to explain the reasons for the u-turn, which came just 48 hours before tomorrow's Commons debate and vote on the UK Government's charter for budget responsibility, which commits to balancing the nation's books within three years and to running a budget surplus every year thereafter.

Last month, Mr McDonnell insisted the new Labour leadership would back the charter in a bid to refute the Conservative charge that it was a deficit-denier.

But at the PLP the shadow chancellor said the party would now vote against the charter tomorrow, and would set out its own plan for "tackling the deficit, not through punishing the most vulnerable and decimating our public services but by ending the unfair tax cuts to the wealthy, tackling tax evasion and investing for growth".

After the meeting, Ben Bradshaw, the former Culture Secretary, could not hide his dismay, snapping: “Absolute f***ing shambles.” Others branded the u-turn a joke.

During the meeting Mr McDonnell also pointed out how the UK party had to "support our Scottish comrades", suggesting that Labour in Scotland would be damaged by MPs going through the Westminster lobby with the Tories and that Mr Corbyn’s initial pro-charter stance was not helping Scottish Labour's anti-austerity policy in the face of SNP criticism.

Nicola Sturgeon tweeted: "So Labour bows to @SNP pressure on austerity charter. Can't believe they previously planned to vote for it. Shows how divided they are?"

Chris Leslie, Mr McDonnell’s predecessor as shadow chancellor, said the u-turn had sent the “wrong message” to the electorate and that Labour needed a "clear and consistent" policy.

He suggested his colleague should instead table a rival motion for tomorrow’s debate and abstain on Mr Osborne's plan, refusing to play his "tactical game".

Mr Leslie warned: "To go from one extreme to the other is wrong in economic terms but also it sends the wrong message to the general public as well. So, to be fair to John McDonnell, this is a very difficult balancing act, it's a very difficult topic, but it's incredibly important that his is clear and consistent and explains fully not just what Labour's position is but why he backed George Osborne's surplus a couple of weeks ago and is now against it, apparently."

The Nottingham MP said the Commons debate was Mr McDonnell’s “first test against George Osborne” and said it was very important Labour's frontbench was “extremely clear about where we stand; people need to know what the Labour Party's position is”.

But, commenting on Mr Leslie's call for Labour to abstain, Angus Robertson, the SNP leader at Westminster, gleefully tweeted: "Shambolic Labour hokey-cokey continues on Tory fiscal charter. First: support. Last night: oppose. Today: abstain!"

Meantime, Diane Abbott, the shadow international development secretary, dismissed the u-turn row as a "process story" and claimed Mr Osborne's legislation was "gimmicky" and designed to put Labour "in a corner".

She insisted Labour was “in the right position now, it is a position that most of the PLP is comfortable with and all party members".

The London MP insisted Mr McDonnell took the deficit “very seriously and the party as a whole takes the deficit very seriously".

Ms Abbott predicted that in 12 months' time the focus would be on Mr Osborne, rather than Labour's difficulties.

"The economy is not going to be in as good a place as it is now in a year's time. People will be focusing on his mismanagement of the economy, not on a ... process story," she argued.

The Shadow Secretary of State, commenting on a stormy PLP, stressed how “at any given time there were will be a group of MPs in Parliament, of whatever party, who are unhappy. I suspect my colleagues, on reflection, will calm down and devote their energies to attacking Osborne and his mismanagement of the economy".

Ms Abbott, a close ally of Mr Corbyn and Mr McDonnell, claimed some in the party were still struggling to accept the result of the leadership election.

"Some people in the party are only slowly coming to terms with the fact that Jeremy won. Once they have come to terms with that, they will be happy," she added.