There we were preparing to thumb through the Cabinet Manual on the “laws, conventions and rules on the operation of government” when the exit poll came through. It suddenly became perhaps the one thing the Conservatives liked about the BBC in this election.

The Labour party wasn’t the only one preparing for a hung parliament, with most polls suggesting Labour would pick up an extra 30 seats south of Hadrian’s wall, and that the Tories would be unable to command the support of the House of Commons, even with the 25 to 30 Liberal Democrats expected to survive.

But Labour’s wipeout in Scotland was the only bit of this election accurately predicted by the pollsters, although even here the scale of our defeat was underestimated.

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The Tories and the SNP deserve congratulations for pulling off a remarkable victory. Ed Miliband fought a decent campaign, but, as with Neil Kinnock in 1992, something went badly wrong at the end – and unlike that election, it wasn’t the exit poll.

The rise of the SNP was unstoppable, despite Jim Murphy’s incredible courage. It was the failure to take seats such as Carlisle and Bury North where we had excellent candidates and a sound organisation on the ground that cost us so dearly.

The remorseless focus of the Tories on the threat of a Labour/SNP tie-up was undoubtedly a significant element in the Conservative victory. It seeped into the public’s consciousness, and was difficult to handle without insulting the intelligence of the electorate – because of course left-of-centre parties would at least talk to one another in the event of a hung parliament.

We in Labour were also strangely quiet about properly funding the NHS. The public would have been mystified as to why all the main parties support a set percentage of GDP being dedicated to international development. The Tories were making noises about meeting the Nato target of 2% of national wealth being earmarked for defence but there was no commitment to return health spending to the European average of 9% achieved under Labour.

But the biggest damage was done on the economy. We seemed to have no effective riposte to Cameron’s successful distortion of our economic record in government. Thus a succession of Tory ministers were allowed to describe the global banking crisis as “Labour’s recession” and to refer (as Jeremy Hunt did) to the economy contracting. There was no rebuttal from Labour pointing out the decent levels of growth being recorded before George Osborne choked off the recovery through his vainglorious emergency budget in June 2010. Nick Clegg’s ludicrous comparison between the bankrupt Greek economy and our own also seemed to pass without question.

There was no rebuttal pointing out the decent levels of growth before George Osborne choked off the recovery

Even the entirely false statement that Gordon Brown had sold off the Britain’s gold reserves at knock-down prices to fund public spending went unchallenged, sacrificed to the strategy of fighting the 2015 election, not the 2010 one all over again. As a result it was open season on Labour’s record in office with the economy front and centre.

Even more perplexing was the fact that we did have a sound economic policy for this election, which we seemed determined to disguise. Our commitment to borrow for capital investment at a time when the cost of borrowing is zero and the economy is still underperforming was a huge and important dividing line between us and the Conservatives that we seemed to want to obscure.

Everyone is entitled to their theory as to what went wrong: mine is that from last week’s Question Time debate in Leeds, where Ed Miliband was assailed about Labour’s alleged overspending, the die was cast. The public became convinced that Labour had indeed driven the car into the ditch and declined to return the keys. While Miliband was valiantly attempting to own the future, he lost the core argument about the past.

The situation now is perilous not so much for the Labour party, but for our country. The Conservatives in office with the SNP rampant north of the border is the worst possible scenario for Britain’s exit from the European Union and Scotland’s exit from Britain.

Only Labour can repel the narrow nationalism of the Conservative right in England and the SNP in Scotland. We need to move on quickly. Harriet Harman has served the party well as interim leader and will do so again. It should not be as long and protracted a leadership campaign as in 2010, and thanks to Ed Miliband it will be the first to be conducted under a genuine one member, one vote procedure.

This is a job requiring an appetite for leadership that I don’t possess, and a commitment to the next 10 years that my age precludes. Fortunately there is an abundance of talent in the parliamentary party capable of ensuring that if this election has been reminiscent of 1992, the next election will recall the one that followed 1992.