A combination of file images show British leader of the opposition Liberal Democrats Nick Clegg (L), Prime Minister, and Leader of the ruling Labour Party, Gordon Brown (C), and Leader of the opposition Conservative party David Cameron Image Credit: AFP

In a hung parliament, the numbers are crucial. What combination of parties can put together a majority on a programme, a bill, a committee stage clause? In any legislature it's the thing that always matters most. Look at Obama's problems with the US Congress. But it's true in Britain too. Numbers are all, and the Conservatives have unquestionably the biggest numbers. First in votes. First in seats. The best position for any party.

The Conservatives have something else going for them too. The elder George Bush called it the Big Mo, and at the haggling, poker-playing stage that will dominate the UK's post-election party politics, this momentum is every bit as important a factor in the calculations as the raw numbers themselves.

Brilliant performance

The Tories are the only party to emerge from the exit poll numbers with forward propulsion. There will be at least 94 extra Tory MPs on the Westminster benches when parliament reassembles. It may be tempting even for some Tories, and certainly for their enemies, to argue that while this is good, it is not quite good enough. It is certainly a tinge disappointing compared with some of the heady Tory talk even on Thursday afternoon. By comparison with anyone else, though, David Cameron's performance has been brilliant. That 6.9 per cent swing needed to take power is a huge ask.

After some of the apocalyptic gloom of the last 10 days, the fact that Labour came in with at least 255 MPs may seem almost miraculous. It is a much larger total than the 209 that Michael Foot managed in the debacle of 1983, and it is a lot more than a lot of Labour people were forecasting in their cups on Thursday.

Momentum, though, casts the Labour figure almost as bleakly as it frames the Tory score in lights. Bloodied but unbowed Labour's platoons may seem to themselves, but there would be at least 88 fewer Labour MPs if the poll is vindicated by the final figures. The overall majority of a month ago has been swallowed up. Gordon Brown is indisputably the 2010 election's big loser.

The Liberal Democrats, meanwhile, suffered the biggest disappointment. All the Cleggmania and all the hullabaloo of the past three weeks will have ended up by producing precisely nothing. Doubtless the eventual results will look a bit different — Lib Dems often pick up seats like Redcar under the radar — but the result looks like being a huge anti-climax for Nick Clegg. In the end the not-Tory-not-Labour vote has fractured to the "others" and not rallied around the Lib Dems as the polls suggested a few days ago.

Put all this together, and two large things can be said. The first is that Brown, who remains prime minister for the moment, is absolutely entitled to talk to other parties to see if he can form a government whose programme would win a Commons majority. All precedent is on his side if he tries. So are Sir Gus O'Donnell's guidelines. So are a succession of unimpeachable Whitehall grandees including Lord Armstrong, who went through all this with Ted Heath in February 1974, and Sir Richard Wilson.

It is an absurdity that the British system does not make this possibility much clearer by stipulating a longer handover period between an election and the inauguration of a new administration. If the outgoing government were allowed to remain in office for a period of a week or so before handing over the reins to its successor, these discussions could take place in calmer circumstances and without hostile self-interested grandstanding from the media and pressure groups.

But the fact is that Britain's system stipulates no such thing. So the pressure on Brown to give up will be intense. He will be accused of trying to steal the election, though he would be doing no such thing. Brown has many faults, but not this one.

I doubt he will be able to get away with it though. The Tories were making clear on Thursday, just as Cameron also said in interviews, that they intend to hustle and hassle themselves into government in such circumstances. Process and precedent would not be allowed to stand in their way. Brown would be framed as an illegitimate would-be prime minister. Cameron seemed to back off from this a little on Thursday night but there is still a clear sense that the Tory and media rolling maul would carry him over the threshold regardless.

Too weak

Even if they wanted to do a deal, Brown and Clegg are too weak in numbers and each too lacking in momentum to succeed in any such enterprise. This may seem perverse. After all, their two parties together are likely to have a clear majority of the popular vote. Yet each has floundered and propping up a loser is lethally dangerous politics. So while Brown is entitled to try to form a government, a weakened Clegg has immense difficulty going along with him. A Lab-Lib deal will have to wait.

The presaged hung parliament is overwhelmingly likely to produce a Conservative government, probably a minority administration ruling with Northern Irish consent.

Be in no doubt that this is a huge personal victory for Cameron. But this is not a Conservative moment in the deeper political sense that Margaret Thatcher's 1979 win was. In time it may become one; but not yet. The result is too close. The UK remains a centrist country, more Cameronian than Conservative.

This is, though, a moment of existential crisis for the centre-left. In other circumstances, under a better leader, the 2010 election was one that Labour might have won or run close. If, if, if. But instead Labour is out of power. Brown may be tempted to hold on as party leader. But Labour needs a new leader with a new outlook.

More important, however, Labour needs to relearn the lessons of 1983. Labour is no longer a majoritarian party, never mind of any progressive majority. There is such a majority in Britain and it may form a government sooner than it thinks. Add the Labour and the Lib Dem seats and shares of the vote together, compare with the Tories and the point is made. But there is not a Labour majority nor one that is Labour's to command. It is a majority that can only be expressed through mutual respect between the two parties and under an electoral system that treats liberal Britain as an equal not an ally of convenience. If there is a positive to be drawn from this election it is that the task of building this partnership can now begin.

- Martin Kettle is an associate editor of The Guardian.