History made as viewers see leaders make their pitches - VIDEO

Three weeks from polling day, they made a direct pitch to millions of voters as they went head to head in what could be a pivotal moment in the election.

In an event constricted by 76 rules agreed between the parties, they were questioned on issues including education, crime, the economy, immigration and Afghanistan.

Liberal Democrat leader Nick Clegg pitched himself as an alternative to the status quo of two-party politics and pleaded with voters not to believe arguments that only the other two could provide the answers, because "we can do something new, something different this time".

He was widely thought to have most to gain from the debate, and initial online polling suggested viewers had responded positively to his performance which ended he was "hopeful" about the future.

Throughout the 90-minute debate, Gordon Brown sought to make the most of his two and a half years as Prime Minister, saying in his opening remarks "I know what this job involves" and finishing by criticising Tory failures to match Labour spending commitments.

Tory leader David Cameron showed contrition over the expenses scandal saying "I'm extremely sorry" in his opening comments before concluding that voters should choose "hope over fear" and ignore the other parties' attempt to scare voters about him.

With ITV host Alastair Stewart struggling to keep order at times as each of the men ignored his attempts to cut them off, there appeared to be early nerves as the contenders were first questioned on immigration and education.

It was over the thorny issue of MPs' expenses the clashes began to get lively, with Mr Clegg, who is seeking re-election in the Sheffield Hallam constituency, condemning the failure to punish some MPs who committed the "big abuses" by flipping their homes for personal gain or avoided paying capital gains tax.

Mr Brown said he had been "shocked and sickened" about the scandal and announced a three-point plan of reform, saying: "Nobody should be standing for election at this election who is guilty of offences we've seen in MPs."

Mr Cameron admitted the scandal had been "horrendous" and said he would cut the cost of politics by slashing the number of MPs by 10 per cent.

As the debate turned to the economy, Mr Cameron clashed with Mr Brown over Labour's planned National Insurance rise and the Tory leader warned the "dark cloud of deficit" was hanging over the country

"People will find it extraordinary to hear the Prime Minister say we've got to carry on wasting money to keep the economy going," he said. "Cut the waste, stop the tax."

But Mr Brown warned the country was at a "critical" point, adding: "We cannot afford to take money out. Taking 6bn out of the economy now would be the equivalent of taking thousands of jobs out of the economy. I would fear for our economy if that happens."

The Liberal Democrat leader hit back, saying: "We need to be open and straight with people. We are the only party in politics saying this is how we'll cut the deficit.

"These two constantly argue about waste as if you can fill the hole in the public finances by saving on paper clips and pot plants at Whitehall."

The issue of helicopters was central to the Afghanistan debate, with Mr Brown denying a helicopter shortage was due to poor planning. Mr Clegg claimed troops were under-equipped and they should be the priority, rather than replacing the Trident nuclear deterrent.

The event was the first of three planned debates, with foreign affairs the subject next Thursday and the economy seven days later.