David Cameron is expecting Thursday's seven-way leaders' TV debate to be an opportunity to show that he stands above the cacophony of minor, mainly leftwing parties, with his aides believing that the event may even impress on voters the dangers of chaos from a left-led coalition.

Bookmakers have Nigel Farage, the Ukip leader, as the likely winner, but a YouGov poll predicts Cameron will come out on top. There are expected to be four snap polls after the debate, including one by ICM for the Guardian.

The two-hour debate, which will be chaired by the ITV news presenter Julie Etchingham, is taking place at MediaCityUK in Salford and it is expected to be watched by up to 10 million people.