Chris Fisher, political editorThe Tories now sense that the force is with them after David Cameron's win in the final TV debate, says political editor Chris Fisher. But can they gain the further ground necessary to secure a Commons majority?Today, May Day, is the 13th anniversary of Tony Blair's first general election victory - an event which led to much celebrating (though Labour won only 43pc of the votes).Chris Fisher, political editor

The Tories sensed that the force was with them after David Cameron's win in the final TV debate, says political editor Chris Fisher. But Nick Clegg could still get very much in their way.

Today, May Day, is the 13th anniversary of Tony Blair's first general election victory - an event which led to much celebrating (though Labour won only 43pc of the votes). A writer in the London Evening Standard wrote the following day that the capital city felt as if it had been liberated.

But there won't be any partying at Labour HQ today to mark the occasion. The partying is over there for the foreseeable future. And the party could well be finished too as a governing force for many a year.

The third and last TV debate between Messrs Brown, Cameron and Clegg has left many imponderables. But it now seems certain, if it didn't already, that it's all over for the prime minister. He threw his best punches on the subject of the economy, but somehow they didn't connect either with the Tory leader or many of the millions of people watching in their living rooms.

He came bottom in almost all the immediate polls. And a Harris poll in today's Daily Mail puts his party right down at 24pc. A YouGov poll in today's Sun gives it 28pc backing.

These results may reflect his debacle this week in Rochdale, but also confirm that much of the electorate has just stopped listening to him. He's like an old heavyweight boxer who's had too many fights and has just been around for too long. He's still standing; he keeps coming back for more; but when he tries to land a blow, nothing happens; and it leaves him feeling bemused and cross.

Labour is now so low in the polls, that outright victory seems utterly beyond it. Indeed, there is a clear possibility that the party which in the Blair decade had laid strong claim to replacing the Tories as the natural party of government, will come third on Thursday in terms of votes. The new Harris poll has the Lib Dems second on 32pc and the YouGov poll has them tied with Labour.

Third in the votes could still leave Labour with a quite a large pile of Commons seats if it were to keep its share of the ballot paper crosses not far short of 30pc. If, for example, the voting shares were Tories 35pc, Labour 29pc, Lib Dems 30pc, the seating allocations would approximately be: 270, 255 and 95.

Even in that situation, however, Mr Brown would be dead meat. He could not preside over the loss of close to 100 seats by his party and cling on inside No 10 as the head of a coalition government; and in any case, Mr Clegg doesn't like him, and can't do business with him.

With such an election outcome, might a Labour-Lib Dem coalition become possible with a replacement Labour leader? It's not at all easy to see how. Who would the replacement be? Could someone - Alan Johnson, perhaps - step straight into Mr Brown's shoes as party leader without triggering a huge internal Labour fight? Who would be the new prime minister - the new Labour leader, or Mr Clegg?

In posing such questions, one cannot gloss over the fact that if Labour sinks to third or a poor second in the vote, it will be a big rejection not only of Mr Brown but also his party. Mr Clegg would inevitably be very wary of being seen to prop it up in a shared government.

If there is to be hung parliament, it now seems it can be only of the Tory-Lib Dem kind. But there are big problems with that too. Mr Cameron doesn't want it, and has so far shown little interest in radical electoral reform; much of his party, moreover, would regard getting into bed with the Lib Dems as only slightly less unattractive than contracting the plague.

Much can change over the last few days of the campaign. The Tories sensed that the force was with them after the Birmingham debate, and hoped to push their poll ratings up from their pre-final debate level of about 35pc to close to, or even above, 40pc. So the latest Harris and YouGov polls will disappoint, if not shock, them. They stand at 33pc in the former and 34pc in the latter.

They must somehow put rocket boosters on now to get away from hung parliament territory and into that of a Commons majority. If, for example, they could get up to 39pc on polling day, the Lib Dems won 29pc and Labour 26pc, Mr Cameron would have a majority of about 15.

Much will depend on whether the Labour vote does sink towards 25pc, or whether it holds up. If, moreover, it does drop, where will the deserting voters go? To Mr Cameron? To Mr Clegg (as Harris suggests)? To someone else? Or will they abstain?

Mr Cameron saved his best till last on Thursday. His core message still eluded me, but he seemed prime ministerial and exuded confidence. He will endeavour to build on that success, and will amplify the message that a hung parliament will mean indecision and extra financial trouble.

Mr Clegg may privately feel disappointed with his performance in Birmingham. He seemed more nervous than in the first two debates, and there was a sense that over three of them his message was spread too thin.

He also got rather skewered - and the danger had always been there - on his party's proposed 'amnesty' for many illegal immigrants.

His task over the next few days? To keep emphasising that the game's up for Labour in this election, and perhaps a lot longer. To stress heavily that the election will bring a very rare opportunity substantially to alter the way things are done at Westminster, and - further to that - to keep challenging Mr Cameron's 'change' credentials. Economic change, certainly. But political change?

Should Mr Cameron really desire a straight victory? Bank of England governor Mervyn King has supposedly warned that the party winning the election will have to inflict so much pain to slash the fiscal deficit that it will be out of power for a generation.

The 1992 election proved a very good one to lose. Next week's could be of the same genre.