ITV leaders’ debate: The biggest danger of tonight's free-for-all – it turns even more people off politics

Matt Dathan previews what could be a make or break moment in each of the seven leaders' election campaigns

This is the first and only time all seven party leaders will be in the same room in the whole campaign and after months of negotiations, bickering and legal threats, they will finally see eye-to-eye in Manchester tonight.

It is the only time Ed Miliband and David Cameron will debate each other – and the Labour leader will try his best to take on the Prime Minister in as many head-to-head arguments as possible to make up for the lack of a two-way TV debate between them.

From left to right: Natalie Bennett, Nick Clegg, Nigel Farage, Ed Miliband, Leanne Wood, Nicola Sturgeon and David Cameron (Sky)

The danger of the seven-way debate is it could end up in a shouting match. The leaders will only answer four questions and after their opening statements, there will be an 18-minute free-for-all argument.

So although tonight’s debate could end up to be the defining moment of the campaign, it could also turn out to be a complete and utter mess.

But the biggest danger is it could turn off even more voters who dislike the ya-boo politics of politicians trading insults across the floor.

Mr Cameron, Mr Miliband, Nick Clegg and Nigel Farage will be careful of coming across too macho in fear of switching off female viewers. And any of them who displays a or 'calm down dear' approach to Nicola Sturgeon, Natalie Bennett or Leanne Wood will be hit hard in the polls.

David Cameroon will be pleased with his position, standing on the far right of all the other candidates, which not only represents where he stands on the political spectrum (compared to all the others apart from Farage) but also gives him an advantage.

When he speaks he will be able to distance himself from the other six and will try and paint them all with the ‘chaotic’ broad-brush approach that he claims they offer. Expect him to calmly stand watching while the other six bicker amongst themselves, and then when it’s his turn he will insist it is only him that can offer stability and “competence”.

The stakes are high – as the only live debate between the leaders, a gaffe by one of them could send their party’s vote tumbling.

On the other hand, a strong showing from Mr Miliband or Mr Cameron could be the turning point in the election campaign and give them the much-needed momentum in the one of the closest election fights in British history.

It is the two leaders who have the most to win and lose because it is only one of those two who will end up as Prime Minister and however impressed voters are with any of the other leaders, there is a limit on how well smaller parties can do in our first-past-the-post voting system.

This is what we saw in 2010 when Nick Clegg shot to fame on the back of his performance in the TV debates, but despite this the Liberal Democrats ended up with less seats than they had before.

But it will still be important for the others. Mr Clegg will try to convince viewers that the election is not just about who should be Prime Minister, but just as important is the kind of government they want.

Only the Lib Dems, he will argue, can offer a balanced approach to government by entering into another Coalition with one of the two major parties.

Ukip’s vote has slid slightly over the last few months in the polls, leading some to suggest their balloon has popped after winning last year’s European Elections.

But Nigel Farage is a popular character, he’s odds-on favourite to win the debate tonight – as he did in last year’s Europe debate with Mr Clegg – and he will take every chance he can to challenge Mr Cameron on his immigration record.

Natalie Bennett will be hoping to come through unscathed – she has struggled under pressure on live TV in the past few weeks over the Green party’s policy costings.

Meanwhile, for Nicola Sturgeon and Leanne Wood, this is a chance to appeal to the whole of the United Kingdom that their parties are a force for good not just for Scotland and Wales, but for all voters.

The Scottish First Minister performs well in this kind of format and will relish taking on Mr Cameron over what she claims are broken promises to deliver Scotland further powers following last autumn’s referendum.

She will face a challenging task to convince Scottish voters to choose the SNP over Labour however when Mr Miliband tells viewers a vote for her party makes a Tory win more likely.

Ms Wood’s Plaid Cymru party are struggling in the polls in Wales but expect her to be among the surprise winners of the debate as viewers suddenly take notice of her eloquent style.

She will benefit from just showing up – few people know who she is and she is an underdog with nothing to lose.