Election TV debates: Will they ever happen again?
In the general election of 2010, the three main party leaders took each other on in Britain's first ever TV election debates, hosted by ITV, Sky and the BBC.
The clashes between Gordon Brown, David Cameron and Nick Clegg dominated the campaign and had peak audience figures of more than nine million.
It had taken half a century to get agreement between Britain's politicians and broadcasters to stage them. Debate about debates has been bubbling away in Britain ever since the US staged the first full-blown televised encounter between presidential candidates John F Kennedy and Richard Nixon in 1960.
Around 80 countries in the world hold debates between those running for national office, including Iran, Mongolia and Afghanistan. But the future of the format in Britain is far from certain.
The path to the 2010 debates was littered with failed negotiations.
In 1964 came the first UK general election after the iconic Nixon-Kennedy encounters. Opposition leader Harold Wilson challenged Conservative Prime Minister Alec Douglas-Home to a TV debate. But Home refused, citing what was to become a familiar objection. "I'm not particularly attracted by confrontations of personality," he said. "If we aren't careful, we'll get a sort of Top of the Pops contest."
Two years later, when he was prime minister, Wilson appeared to have a spectacular change of heart about debates, turning down challenges from the new Conservative leader, Ted Heath.
And so began a pattern of U-turns as political self-interest dominated any principled arguments. Other examples include the Conservative Prime Minister John Major, who went from apparently principled refusal in 1992 to challenging the Labour leader Tony Blair to a debate in 1997.
Mr Blair's promise to debate with John Major "any place, any time" rapidly evaporated in failed discussions.
The BBC's chief political adviser, Ric Bailey, who was on the broadcaster's negotiating team for the 2010 debates, said: "Political parties only want to go for something like this if they think there's political advantage in it for them. If you're the incumbent, you don't want to put yourself on the same footing as your rivals. If you're way ahead in the polls, why would you risk that by throwing yourself into something as unpredictable as TV debates."
After the 2001 election, in which Tony Blair rejected debates for the second time, his aide Lance Price admitted: "We were never up for it. We were way out ahead in the polls. It wasn't a question of whether or not we would agree; it was a question of when and by what means we would get out of it."
Although many remember America's 1960 debates, what is less well known is that they were followed by a 16-year gap.
Professor Alan Schroeder, from Northeastern University in Boston, explained: "These live debates are so terrifying to the politicians that they really don't want to have to do it. After Kennedy and Nixon, and it had been such a devastating experience for Richard Nixon in particular, politicians were very gun-shy about going into the debate arena."
When, in 1976, President Gerald Ford bucked that trend in agreeing to debate with Jimmy Carter, he may have wished he hadn't. His claim that there was "no Soviet domination of eastern Europe" caused consternation around the world, not least in Soviet-dominated Eastern Europe.
But since then, debates in the US have become part of the political culture, however much some politicians might wish it otherwise.
In the UK, the future of the format is far from certain. Although the 2010 debates were popular with voters, many politicians are less convinced. Conservative critics point to the destabilising effect of the "Cleggmania" phenomenon, when the Liberal Democrats' support surged after the first debate. Some have even suggested the clashes played a part in David Cameron's failure to win an overall majority.
Tory backbench MP Conor Burns is urging his leader to think twice about taking part again in debates on the same format: "For David Cameron to exceed the expectations people will have of him will be very hard, if not impossible. For Ed Miliband to exceed the expectation the public have of him will be relatively easy."
Mr Cameron is facing pressure to make clear his position on the debates, including from the Labour leader, Ed Miliband, who said he would "relish" taking part. The prime minister has said he is in favour in principle, but has not clarified the details.
One suggestion he and other Conservatives have made is to stage the debates before - not during - the election campaign, an idea which would not appeal to the broadcasters.
The BBC's Ric Bailey, although a debate enthusiast, warned: "There's no guarantee. The people who are most pessimistic are usually those who negotiated them because they know how many things can go wrong."
"My gut feeling is they're unlikely to happen in the way they happened last time," said Tory MP, Conor Burns. "People can always find a formula as to why they shouldn't happen."