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After all the to-ing and fro-ing over whether leaders' election debates would happen and what format they would take, Thursday night sees the only genuine television debate in which the prime minister will take part.

But how will each leader make the best impact?

Andrew Caesar-Gordon, managing director of media training company Electric Airwaves - one of their trainers advised Nick Clegg before the last debates in 2010 - said the leaders won't have much time to develop complex arguments in tonight's debate.

They'll be looking to craft sound bites and catchy one-liners, known in the US as "zingers" - as these will be crucial in the next day's coverage.

But Diana Mather, etiquette and media coach, sounded a note of caution against the leaders being rude, as "it really turns people off" - citing Prime Minister's Questions as an example.

She said politeness would help them to come across as more natural and passionate.