Scottish Labour's collapse was "a disaster waiting to happen", according to former UK party deputy leader Dame Margaret Beckett.

Her inquest into the reasons for the party's defeat in the 2015 general election said the party failed to anticipate a rise in SNP support after the 2014 independence referendum.

Labour casting its die with the Conservatives in the Better Together campaign also hurt the party's electoral chances, she found.

There was also a perception Ed Miliband was not as "strong a leader" as David Cameron and he might need to be "propped up" by the SNP in government.

Labour was "badly beaten" in 2015, the report acknowledges, and faces "huge challenges" to have a hope of winning in 2020, when the effect of boundary changes, an ageing electorate and the apparent entrenchment of the SNP in many of its former Scottish strongholds will make defeating the Conservatives even more difficult.

The report reads: "Labour had been the dominant party in Scotland for many years after the near death of the Tories.

"It is widely believed that our collapse there was a disaster that had been waiting to happen, perhaps for many years.

"The referendum victory was a relief for the cross-party Better Together campaign. Because the referendum was cast, inevitably, as a Yes or No campaign, Labour and the Tories ended up on the same side, in support of the union.

"What no one envisaged was that, immediately after the result, the Prime Minister would choose to play the English nationalism card, with a dishonest, as well as unscrupulous, call for English votes for English laws, when all experienced parliamentarians know that, only rarely, is there any law affecting only England.

"Labour strongly dissociated itself from such a dangerous manoeuvre. Perhaps in consequence, few realised that support for the Yes campaign might lead straight to increased support for the SNP, especially as their policies, on, for example, the top rate of tax, or a mansion tax, were more conservative than those of Labour.

"In fact, while some might have expected Labour to regain support after the referendum, the SNP adopted Labour policies they had previously rejected and built not only on the emotion of the referendum but on the perception of a possible betrayal of government promises."

Releasing the Learning the Lessons from Defeat taskforce report, Dame Margaret said: "The reaction to the 2015 result was inevitably an emotional one for Labour because it was such a surprise.

"There was certainly no complacency in the Labour ranks but the polls showed us neck and neck with the Tories when clearly we weren't.

"There are certainly lessons to learn from defeat. This report has been a key part of recognising areas we need to improve on and building on aspects of our campaign that performed well."

She added: "The road to re-election is a marathon, not a sprint. If we learn the lessons of defeat in 2015 we can take the steps needed to rebuild a society in which the common good and greater prosperity for all go hand in hand, and elect a Labour government."