DAVID Cameron won the final leaders’ debate by a clear margin last night, as the Prime Minister’s chances of re-election faded into the distance.

Labour aides acknowledged that the debate on the economy marked the last opportunity for Gordon Brown to save the party’s flagging fortunes, but nearly all the instant opinion polls had him trailing in third place.

An average of five opinion polls put the Conservative leader on 35 per cent, Liberal Democrat leader Nick Clegg on 32 per cent and Brown on 26 per cent. All but one showed Cameron as the clear winner.

In the third and final of three lengthy 90-minute debates, the leaders traded blows on spending cuts, banking reform, immigration, housing shortages, education and benefit fraud – but the country’s yawning £163bn deficit was barely mentioned.

Aware that the Liberal Democrats now pose the biggest challenge to his chances of securing an overall majority after 6 May, Cameron focused many of his attacks on Clegg.

“People need to know the Lib Dems are still in favour of joining the euro. If we were in the euro now, your taxes would be going to Greece,” he said, in the only reference to the fiscal crisis that is rocking Europe.

And he attacked the Lib Dem policy on an amnesty for illegal immigrants as “profoundly misguided”, in a series of heated exchanges a day after the issue took centre stage when Brown called a voter “bigoted” for raising the topic.

Clegg hit back at Cameron, snapping “why don’t we save time and just assume every time you speak about our policies you are wrong.”

The Lib Dem leader continued to cast his rivals as standard-bearers of the “old politics”, with an impassioned closing statement where he made a direct appeal to voters.

Clegg said: “Don’t let anyone tell you it can’t happen – it can. This time you can make the difference.”

Brown gave by far his strongest performance, acknowledging the disastrous “bigot-gate” gaffe in his opening remarks. “As you saw yesterday, I don’t get all of it right. But I do know how to run the economy in good times and in bad,” he said.

Aware he had little to lose, the Prime Minister went on the attack, warning voters that Cameron and Clegg posed “too big a risk to the economy”.

However, all but one instant opinion poll put him a distant third, while his final statement acknowledged that Labour is unlikely to win the election unless it pulls off a remarkable game-changer.

“I know that if things stay where they are, David Cameron, perhaps supported by Nick Clegg, will be in office,” he said.

Meanwhile, Labour last night revealed that Tony Blair, the former Prime Minister that took the party to an unprecedented three election victories, will start campaigning for Brown this week.