General election 2017: Do TV debates matter - and will they make a difference to the results?

ITV has thrown down the gauntlet to Theresa May and Jeremy Corbyn with the announcement it will hold a leaders' debate in the run-up to the general election.

Invitations have gone out to both politicians for the 18 May showdown, along with the heads of the SNP, the Liberal Democrats, the Greens, Plaid Cymru and Ukip.

However, the Prime Minister has already said she preferred to "knock on doors" and meet voters instead, leading her Labour counterpart to say it would be pointless to participate in her absence and he would not attend without her.

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Speculation that the broadcaster would "empty chair" non-attendees, a move seen as designed to shame those who do not show up, appears to be just that - Radio Times says spaces will only be provided for those who agree to turn up.

Following a public outcry - leading the Daily Mirror to send a reporter in a chicken costume to follow the PM on the campaign trail, as it did when David Cameron also tried to avoid debating in 2015 – the Prime Minister has since indicated she might take part in a question and answer session with a TV audience, the Daily Telegraph reports.

What is the history of TV election debates?

While a staple in the US, TV debates are fairly new to the UK.

ITV broadcast the first one in 2010, when 9.4 million watched Cameron battle it out with Labour's Gordon Brown and Nick Clegg of the Lib Dems.

Clegg was widely regarded as having stolen the show, with the resulting "Clegg-mania" boosting both him and his party.

Tom Mludzinski, head of political polling at ComRes, told the BBC: "[TV debates] can be a particular help where things are unknown - that's what we saw with Nick Clegg.

"He had a much lower profile back then and that exposure created the 'I agree with Nick' phenomenon and so-called Clegg-mania."

However, Cameron later said the debate format "sucked the life" out of the campaign, reports The Guardian, and he refused to take part in the BBC's televised debate in 2015, despite Labour leader Ed Miliband calling for a head-to-head.

Miliband was instead left to battle in a "challengers' debate" with Sturgeon, Leanne Wood of Plaid Cymru, the Greens' Natalie Bennett and Nigel Farage of Ukip.

Cameron did, however, agree to participate in ITV's seven-way debate - in which Sturgeon and Farage won plaudits for their performances, while Miliband proved unpopular with watching voters.

Do TV debates influence elections?

With such a short track record, it is hard to tell just how much difference a debate makes to the electoral outcome. Clegg's ratings jumped from less than 20 per cent to 33 per cent after the three 2010 TV debates, but this did not translate into as many votes as he might have hoped and the Lib Dems' number of seats went down from 62 to 57 in the election.

Nevertheless, the electorate is clearly keen: a YouGov poll in 2015 found almost seven in ten voters (69 per cent) wanted televised debates, while only 19 per cent disagreed.