Chris Fisher reflects on the second leaders' TV debate

Nick Clegg essentially consolidated his party's remarkably high ratings in the polls; David Cameron bounced back and gave the Tories a potentially decisive lift; and though now usually third in the polls, Labour - thanks to the idiosyncrasies of our electoral system - could yet emerge from the election with the largest total of seats.

In short, after the second of the leaders' debates on TV, each of the three main parties had something to keep its spirits up - even Labour, though its poll figures are virtually down to the level it sank to under Michael Foot in the 1983 general election, and it now needs a miraculous Lazarus-like revival to keep a Commons majority. Its smiles are coming mainly from the prospect of a hung parliament and of the Tories not winning many (if any) more seats than it will.

The second TV debate was markedly different from the first in character and in terms of the scores awarded to the protagonists. The Lib Dem leader was widely thought not only to have won last week in Manchester but to have done so by a considerable margin. But in Bristol it was a much closer run thing. Some of the immediate polls said Mr Clegg had just edged it, but others said the same for the Conservative leader; the PM came bottom in all of them, but generally not by much, and there was recognition that he had performed better than a week before.

Mr Cameron still seemed to be searching for a central theme after the "Change" message had been Nicked from him, but he was more confident, assertive and authoritative - repeatedly saying "if I was your prime minister" - than in the Manchester debate. Mr Brown played to his strengths, and had a good start in saying: "If it's all about style and PR, count me out. But if you want someone to make decisions, and with the judgment and a plan for the future, I'm your man."

Mr Clegg was on good form again - but fell a bit short of his Manchester performance. He missed some opportunities. By my counting he mentioned Iraq only twice; he could have done more to try to turn the difference between him and the others on Trident to his advantage; and his answers on green issues and the forthcoming papal visit had too little substance and too much waffle. When he came under fire, moreover, over his party's proposed amnesty for illegal immigrants, it sounded as if he was struggling to overcome reservations in his own mind.

Had he had a second clear win, his party could have soared into the high 30s in the polls, and we would then have been on course for an election result that even the most ardent Lib Dems might have hesitated to fantasize about; a 37pc share of the vote on May 6 could give their party about 200 Commons seats. There has been polling evidence, moreover, that they could get into the electoral stratosphere if there were a real chance of their winning the election; one survey indicated that in those circumstances they could obtain 49pc of the votes.

Mr Clegg's achievement in Bristol was instead to hold on to the poll gain he had made the week before. That was still much to his credit, but it could actually prove to be the start of a significant decline for his party's poll ratings. Sometimes, momentum is everything, and standing still is a prelude to going backwards. Mr Cameron defended the Tory castle against further damage by the "yellow peril", and may now be able to start reversing last week's tide.

The Lib Dem leader is still seriously in contention in the election race, but it has just been underlined that he is not (almost certainly) going to win it. He is fighting not to win the crown but to become the kingmaker and to extract a high price from the man and party he chooses.

We remain deeply in hung parliament territory. After the Bristol debate there were poll of polls figures of Labour on 28pc, Conservatives 33pc and Lib Dems 30pc. These translate approximately into 265 Commons seats for Mr Brown's party, 255 for Mr Cameronand 100 for Mr Clegg's. (Yes, in this scenario Labour comes third, yet wins most seats. The deficiencies of first-past-the-post would become much more obvious - and politically unsustainable - if it turned into third-past-the-post wins.)

Even if Labour stays down at 28pc - a very big 'if' - the Tories will need to get their voting share up from 33pc to about 39pc and the Lib Dem share down from 30pc to about 25pc to secure a Commons majority. And in the 12 days that remain of the campaign, that is a huge ask.

In confirming that the economic recovery is weak, yesterday's GDP figures allowed the prime minister to return to his favourite policy area with confidence of getting the better of the argument with Mr Cameron and shadow chancellor George Osborne. And the economy is the main subject in the third and final leaders' TV debate this coming Thursday in Birmingham. Mr Brown will be disappointed if that doesn't boost him in the polls, and even a modest rise for him could make a Commons majority yet more elusive for Mr Cameron.

Lord Mandelson and some other senior Labour figures have been blowing kisses at the Lib Dems for quite a few days in anticipation of a hung parliament, and the formation of a coalition government. It has been combined with some Lib Dem-bashing, and a hung parliament would carry some very big problems from a Labour perspective. It is virtually inconceivable that Mr Clegg and his colleagues could work in an administration led by Mr Brown. But how would the electorate react if he were thrown out and replaced as prime minister by another Labour figure? The Labour overtures about a hung parliament also smack heavily of desperation, and Mr Cameron and his team are not there yet. He consequently is still loath to countenance the possibility of such an outcome. But if the Clegg bubble doesn't burst, it's going to happen - and a radical and rapid Conservative rethink could then be necessary.