Senior Conservatives and Liberal Democrats believe the next few months will be the most traumatic the Coalition has faced. Not only will the Liberal Democrats most likely have lost AV, there are bruising rows to come on directly elected police chiefs, the NHS and House of Lords reform.
In public the Liberal Democrats will emphasise that tackling the deficit is their priority. But some in the party (including Cabinet members) may argue, if growth does not pick up, that the cuts go too far. That could spell the end game and an early election.
And if there's a Yes vote in the referendum Equally troubling for the Coalition – but it will be the Tory right not the Liberal Democrat left who will be on the warpath.
The Deputy Prime Minister will accept that he and his party have failed to persuade the public of the case for electoral reform. But he will insist that the party did not go into Coalition "for sweeties" and will emphasise the Government's wider reform programme including tax changes, the pupil premium and the "Green Deal".
But this will be a torrid time for the Liberal Democrat leader. The worst case scenario is that 75 local Liberal Democrat parties get together and hold no-confidence votes in his leadership – triggering a leadership election. That is unlikely. But defections to Labour, some possibly at a senior level, are not.
If there's a Yes vote: Clegg's position in the Liberal Democrat pantheon of heroes is assured.
The Prime Minister (and those around him) will do everything they can to prevent Tory gloating. There was an agreement between Cameron and Clegg before the campaign that whoever won would keep their side in check. In private Cameron will try to repair some of the personal damage done to his relationship with Clegg by the bruising campaign. Expect a private acknowledgement that Clegg needs more latitude to criticise Cameron in public.
And if there's a Yes vote Calamity for Cameron. Not only will he have failed to win an election, he will have miscalculated terribly by handing the Liberal Democrats the referendum.
A No vote is not good news for the Labour leader. His party is expected to do badly in the Scottish elections and the right-wing press will portray today's results as two losses out of three for Labour (presuming they do well in council elections). Expect Miliband to say the problem with AV was Clegg. But he can't get round the fact that his inability to get his party to support him on AV was a decisive factor in the result.
And if there's a Yes vote He will claim that he won it for AV despite Clegg.
The Liberal Democrats
AV was the big prize for going into government with the Tories and now it has slipped away. At the last two Liberal Democrat conferences there were predictions of internal dissent that did not come to pass. This September may be different. The problem the party has is where to position itself: it finds it more difficult to position itself as a social democratic alternative to Labour, but is there enough space on the progressive right?
Rebellion will be constrained by the knowledge that the party now has little choice but to stick with the Coalition and hope to reap the political benefits of successfully reforming the economy by 2015. But will individual members – and defeated councillors – stick with it?
And if there's a Yes vote Ecstacy –and renewed vigour to fight for full PR.
For those who have spent years campaigning for a truly proportional system to elect MPs, this is a deeply depressing day. Never truly comfortable arguing the merits of AV, they have now lost the chance of achieving full proportional representation for at least another two elections, if not a generation.
And if there's a Yes vote Step up to campaign for full PR after 2015.
Also a bad day for Colin Firth, Stephen Fry and Eddie Izzard when you're outgunned by John Prescott and Margaret Beckett. We'll see less of the "A-listers" in the future.
And if there's a Yes vote: Arise Lord Izzard.
mps in safe seats
Will breathe a sigh of relief. The days when they can weigh their votes rather than count them are not over.
And if there's a Yes vote They will have to hope that Lords reform is dead.