Let’s start with detail and work up to the big picture.

Detail number one is the manner of Scottish Labour’s wipeout by the SNP. Detail number two is the complex voting shifts that denied Labour most of the midlands and southern English marginals it needed to get within striking distance of a coalition. Detail number three is the collapse of the Lib Dems.

The SNP’s victory was not made by Nicola Sturgeon, although together with Nigel Farage she was one of the few prominent politicians able to confidently exude plausibility and do populism. The SNP’s victory was wholly manufactured by Labour.

Scottish Labour convinced itself that the separatist mood was being driven by economic grievance. But most journalists who covered the Indyref quickly realised it was about a positive identity, total rejection of the austerity politics that Labour had signed up to, and essentially a form of plebeian national leftism.

Labour not only had no answer to this – it refused to recognise the problem. So it responded to the 45 per cent Yes vote by installing Jim Murphy as leader, using the party machine to squash its usual bugbears – the left, the unions and those seen as soft on separatism.

Murphy then duly tried to redraw Scottish Labour as a slightly left-wing unionist party.

On this basis senior Labour figures were predicting even on the eve of the poll that they would stem the SNP’s advances. The strategy was smashed to pieces by the Scottish electorate.

When we look at the way Labour’s forward march was halted in England it becomes clear how heavily the Scottish dynamic had begun to play in the English marginal.

In seat after seat that Labour held you get a Lib Dem collapse, a holdup of the Tory vote, and a 4-5,000 surge for Ukip.

My hunch is that the Lib Dem votes went mainly to the Tories – and that a lot of it was tactical in response to pleas by the Conservative press for tactical voting to avoid a de facto Labour/SNP majority.

The Ukip surge clearly came largely from Labour voters – as evidenced by the close shaves Labour had with Ukip in Hartlepool and Heywood and Middleton.

What does this tells us?

Labour in England was fighting a campaign about fairness, less austerity and the NHS. But the SNP surge made the debate exactly about what Cameron said it was: who can form a non-chaotic and legitimate government of the UK.

Having been told the SNP were akin to a Scottish Sinn Fein by the Labour leadership, once this became the salient issue, Labour’s heartland economic agenda had no traction.

And make no mistake, a significant section of working class labour voters are still not convinced on freedom of movement. That – not Euroscepticism – is what is driving the Ukip vote in the north and in Wales.

The third bit of detail worth exploring is the Lib Dem collapse. In the metropolitan middle-class areas – especially London – it reflected a return to Labour.

But the Lib Dems’ woeful performance in government – their dithering ministers who never seemed to affect anything decisive – seems to have sapped their will to live in many constituencies.

If you add up all the details what do you get? Scotland has voted decisively for a party that wants to leave the union, and which rejects austerity. It has gone left, towards a confident internationalist populism.

That leaves Labour in existential trouble. Labour’s Scottish contingent was not just some minor offshoot. It was, together with Wales, the ballast that anchored it to what I’ve called “post-industrial Britain”.

To get a Labour majority government, given the political weight of liberalised conservatism in southern England, you need the English north, the industrial Midlands, most of Wales and most of Scotland.

Labour shadow ministers who sneered at the idea they might offer Proportional Representation to the Libdems, on the eve of the election, will now have to face the fact that only permanent coalition politics or electoral reform can give them a chance to rule in future.

I’ve said, from the very start of this campaign, that there are two confident forces in British politics and one deeply challenged one.

Scottish left social-democratic separatism is confident. In the asset-rich south, Cameron-style Conservatism is also confident. Labour no longer knows what it is for, nor how to win power.

But it does know how to fight old battles. All around me, as I write, the SMS and Twittersphere is abuzz with a nascent battle between Blairites and ex-Brownites. There’ll be calls for a return to Blairism – on the grounds that only politics that can “reach across the class divide” can work for Labour.

But it’s no longer the class divide that’s most important. It is the emergence of Scottish nationalism and the protective reaction it’s produced in England.

And quite how a new Blair would reach out to the Ukip voters, the very people Blairism assumed would always vote Labour, is not clear. In addition, an overt Blairite candidate has no chance of running the party without the biggest union, Unite, leaving.

Labour will wake up to quite a decent swathe of red across the north of England and the south of Wales. But in its current form it has almost no ideological base, or coherence.

Miliband’s innner team had almost no outriders in the press, no co-thinkers in academia; they had support among artists and film directors, but always half-hearted.

Blairism, of course, has massive support among the now wrinkled and pensioned ex-ministers and former giants of 1990s journalism, but that’s not much use.

Labour today is waking up to something much worse than failure to win. It has failed to account for its defeat in 2010, failed to recognise the deep sources of its failure in Scotland, and failed to produce any kind of intellectual diversity and resilience from which answers might arise.

Watch: the extraordinary moment when The Labour Party campaign chief Douglas Alexander realised he’d lost his seat to Scottish National Party (SNP) 20-year-old politics student Mhairi Black by six thousand votes.Watch more: Douglas Alexander’s concession speech here: https://www.youtube.com/watch?v=o7-ZMZeR6a4 Posted by Channel 4 News on Thursday, 7 May 2015

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