Reading Labour Party nominates both Jeremy Corbyn and Owen Smith

Smith said on Tuesday he was “as left wing” as Corbyn and was “massively” to the left of Blair.

In a series of messages on Twitter she said Mr Corbyn’s position was untenable and warned: “If we’re not united, we’re doomed”.

Had the rules meant to suggest an incumbent leader did not need the support of MPs, “we would respectfully suggest that would have been so important it would be said in the terms [of the party rules]”, Millar said.

Corbyn lost the confidence of the bulk of his colleagues in parliament but has refused to stand down, citing the overwhelming support from members during the party’s leadership election in September.

“I suspect that Jeremy has got a rather more metropolitan sense of that and that’s not one I think is central to the Labour tradition”.

Polls suggest that Mr Corbyn is favourite to win the leadership contest.

Asked whether there are too many migrants living in Britain he replied: “I think it depends where you are is the truth”.

The former shadow work and pensions secretary also dismissed Corbyn’s claim to have forced the Conservative government to U-turn on cuts to tax credits and other welfare policies. “I have never seen a more bleak or depressing picture than what confronts us now”, he said.

The announcement comes amid a High Court battle over whether Mr Corbyn should be automatically included on the Labour leadership ballot paper.

ICM’s Martin Boon added: “Clearly, the relative calm associated with the handover of power from David Cameron to Theresa May, allied to the current Labour leadership challenge weighs heavily on electors’ minds”.

The ICM poll showed Ukip as the third force in British politics on 13 per cent, the Liberal Democrats on eight per cent and the SNP and Green Party on four per cent each.

ICM interviewed 2,012 adults online between July 22 and 24.

His warning came as Mr Smith said Mr Corbyn and shadow chancellor John McDonnell’s aides breached parliamentary privilege if they entered a Labour MP’s House of Commons office without permission.

It said: “The next general election has already begun”.

Mr Smith described Seema Malhotra’s claim as an “internal little spat” but said staffers should not have entered the former shadow minister’s office without her permission.