Jim Murphy has warned the SNP will force another Scottish independence referendum when they "can get away with it", thinks social media can be "brutal and vile" and admitted Labour's need to have an "honest reckoning our past" has included reconciling with Ed Balls.
The former Scottish Labour leader and Cabinet minister today gave his farewell speech as he stood down from frontline politics, delivering a series of damning verdicts on both Labour and its opponents.
He blamed the SNP landslide on David Cameron creating a "grievance" in Scotland with Westminster that is still fuelling division.
Mr Murphy, a lightning rod for criticism from SNP supporters, said the rise of politics being debated via Facebook and Twitter has led to the "welcome demise in deference" but "at times abolishing manners too".
He went on to warn the Labour Party against "blaming the voters" for its thumping election defeat, and "confessed" he was guilty of the "self-indulgent and self-destructive" in-fighting between supporters of Tony Blair and Gordon Brown that it has to leave behind.
Mr Murphy, a Blairite, admitted he spoke to Ed Balls, a leading Brownite, more in the last two months of the election campaign than in the last two decades.
"I realised how wrong I had been," he said, hinting at a reconciliation. "I had no closer support from any colleague during the election than Ed Balls."
Mr Murphy was at the helm as Labour were swept away by the SNP in May's general election in Scotland, leaving his party with just one MP and the nationalists bagging 56 of the 59 seats north of the border.
The former East Renfrewshire MP was hailed by unionists for his referendum stump speeches atop Irn-Bru crates, but latterly became a target for nationalists in the general election who labelled him a "Red Tory" for campaigning alongside the Conservatives.
Speaking at the Policy Exchange think-tank in London two days after standing down, Mr Murphy hit out at Mr Cameron for announcing he wanted to limit the power of Scottish MPs just hours after the referendum result.
By quickly pushing for "English Votes for English Laws" the Prime Minister created a "grievance" that has succeeded "beyond his wildest ambition", the "full force" of which was no felt until the election campaign.
"It meant that by the time the election came I felt that we were campaigning against a quasi-religious rock concert," he said, meaning messages were falling on deaf ears.
He said Labour "paid the price for doing the right thing" by campaigning with the cross-party Better Together group, but it was a "mistake" to leave "very little identifiable" that Labour could put its own name to, including Gordon Brown's 11th hour tub-thumping speech.
Underlining he has no regrets, Mr Murphy said: "If I had my time again I’d climb on board my two Irn-Bru crates to campaign for the union all over again.
"And if we're not careful another referendum will be upon us as soon as the SNP think that they can get away with it."
He added one of the failures was the Scottish Labour Party had "no plan for after the victory" while the SNP "spent the post-referendum period in a perpetual lap of honour around the winners enclosure".
Mr Murphy joked during the speech it was great to come to an event where "I don't have to fight my way into the room" and "where the police aren't arresting people", a reference to a rally in Glasgow that he was forced to flee from.
He alighted on social media "giving voters a direct connection with politicians" and changing the "very nature of political discourse", but that it has side-effects.
He added: "A new directness that has heralded a welcome demise in deference. But also at times abolishing manners too. At times the anger at powerlessness meshes with the directness of social media to create a brutal and vile conversation."
Issuing a plan for Labour's revival, he made clear the party has to reach beyond its core vote, adding he was "one of the far too few people in the party" who does not want to forget about the Tony Blair years.
And he urged them to remember the "first law of politics": "Voters never get it wrong."
"When you lose on the scale that we did this year then some reflection is needed," he said. "If you decide to blame the voters, you’re wrong.
"To wrest power from a Tory majority, Labour must do what it has always done when it wins a majority - win Tory seats by winning Tory votes."
And he warned the Labour leadership hopefuls against condemning Ed Miliband in the way the 2010 contest was marked by candidates disowning Mr Blair, despite being one of "only two of the last nine Labour leaders have won elections".
He said: "This shouldn’t be about who can run furthest from Ed Miliband. But about who can travel fastest towards the British people."
He said the leadership debate has to reflect the "depth of our defeat" rather than "one more heave" in the same direction.
He said: "This has to be a contest about what we should do and not just a confession about what we didn't do. Not just a lengthy mea culpa.
"However good that is for the spirit, a living, breathing political party needs far more. Bluntly, we need a reckoning with our past."