Tom Harris, the ex-Glasgow MP, has warned Jeremy Corbyn, whom he dubs the “Islington Messiah”, that if he expects his brand of hard Left socialism to revitalise Scottish Labour, then he will be sorely disappointed.

The former Transport Minister, claimed that, as in England, the hard Left represented a “tiny sliver of public opinion” in Scotland and pointed out the SNP had not triumphed north of the border because of their appeal to the hard Left but to the moderate centre.

Mr Harris, who now runs a public relations company, argued these voters, who decided every election, would “take some persuading” that they should abandon what had become, in the SNP, the safe, moderate, competent option in favour of a radical form of socialism belonging to a bygone era.

He pointed out that when Michael Foot surprised Britain by becoming the Labour leader in 1980, the first polling showed the Opposition led the Tories by six points; this week, the first poll undertaken after Mr Corbyn’s win showed Labour six points behind them. Very few Labour MPs, Mr Harris contended, could envisage that situation improving much, if at all.

He added: “If Scottish voters, even those who approve of Mr Corbyn’s politics, don’t believe he can beat David Cameron or his successor as Tory leader in 2020, they will conclude that the answer to both questions - who will best protect Scotland from the Tories and who stands up best for Scotland - is the same as the answer they gave in May: the SNP.”