SCOTTISH Labour's refusal to back a second question on the independence referendum ballot paper was a major factor leading to the party's crushing election defeat last month, a leading union boss has claimed.

Pat Rafferty, Scottish Secretary of the powerful Unite union, said Labour would have entered the election "with the people's faith intact" had the party campaigned successfully for more Holyrood powers during last year's independence vote.

He argued Ed Miliband, the former Labour leader, might have become prime minister if Labour had not "arrogantly" supported a straight Yes/No vote.

Mr Rafferty used an article for the Labour List website to hit back at claims by some within Scottish Labour that his union failed to support the party and undermined Jim Murphy's leadership.

He dismissed the claims and traced Labour's disastrous election result, when its tally of 40 Scottish MPs was reduced to one, to its decision three years ago to back a Yes/No vote on independence.

Former First Minister Alex Salmond was privately keen on a second question and encouraged trade unions, charities and other "civic Scotland" bodies to press for a ballot paper option that offered more powers for Holyrood, short of independence.

Mr Rafferty said Unite pleaded with Labour to back the idea, "only to be dismissed out of hand, with Scottish Labour displaying the arrogance of which it is so oft accused".

He added: "Just reflect for a moment if we and others had been listened to.

"Devo Max would have won comfortably in the referendum with Labour at the head of that campaign, able then to go into the general election with the people's faith intact.

"There would have been no need for Better Together, no terrible taint left on Scottish Labour.

"The electricity and momentum of the Yes campaign would have been subdued.

"The SNP may have gained some seats on May 7, but Labour would have held on to many.

"Maybe we would now be talking about Prime Minister Miliband."

Those in favour of a second, 'more powers' question failed to persuade any of the main parties to back the idea officially.

No concrete proposal for a package of powers to be devolved, which Scots could vote on, was ever agreed.

Unite favoured devolving a broad range of tax and welfare powers to Scotland, leaving defence, foreign affairs and the currency as Westminster's main responsibilities north of the Border.

In his article, Mr Rafferty also rejected claims his union continued to oppose Mr Murphy's leadership after he was elected last December.

The union backed left wing rival Neil Findlay for the top job, fearing Mr Murphy would alienate the party's core supporters.

But he stressed: "Once elected, Unite made it clear that we fully backed Jim and genuinely hoped our worries would be proved baseless".

He said Unite general secretary Len McCluskey's outspoken criticism of Mr Murphy "hasn't stopped him and Unite committing fully to Labour's cause".

Mr Murphy fired an angry parting shot at Mr McCluskey when he announced his decision to quit last month.

He rejected claims his leadership had cost Labour the election across the UK as a whole and claimed Unite would "back the wrong horse in a one-horse race".

He said Mr McCluskey was the "kiss of death" for Labour.

Mr McCluskey hit back, accusing Mr Murphy of using him as a "bogeyman".