The Scottish independence referendum left Labour’s hopes of winning last year’s general election “unachievable”, according to an internal party report.

The official Labour inquiry, led by Dame Margaret Beckett, concluded that Labour had a shot at re-election, especially after David Cameron failed to win an outright victory in 2010.

But that chance disappeared with the fall-out from the 2014 independence referendum, which led to a surge in support for the SNP north of the Border.

The report states: “Our view is that the seeds of defeat were sewn far before the short campaign.

“Ed Miliband and the party had stated an ambition to return to power after one term in opposition.

“In retrospect, while this may have been achievable in 2010 - given the Tories failure to achieve an overall majority - it was unachievable after the fall out of the Scottish referendum, regardless of leader and strategy.

“The potential outcome of forming a minority government depended on greater success in our target seats, but was also affected by the scale and nature of the Liberal Democrat collapse.

“In truth the defeat was only a shock because the opinion polls were so inaccurate in predicting the overall vote share of Labour and the Tories tied at 34 per cent-34 per cent.“