Previous attempts to get leaders to do a TV debate have failed
Gordon Brown is facing renewed calls to take part in a TV debate between party leaders in the run-up to the next general election, expected next spring.
He has previously rebuffed calls saying there is a weekly debate at prime minister's questions.
But Sky News says it will host a live debate and will "empty chair" any leader who does not take part.
Tory leader David Cameron and Lib Dem Nick Clegg say they will take part but Mr Brown has made no such commitment.
In July Lord Mandelson - the first secretary of state - said he was open to the idea but it was up to the prime minister to decide if he wanted to participate.
Opposition leaders regularly call for TV debates in the run-up to general elections but while they are commonplace in the US, they have not been held in Britain.
Tony Blair refused to take part in one when he was prime minister and Mr Brown has previously argued that the situation is different in the US, where presidents are directly elected.
He has also said he is questioned regularly, at prime minister's questions and in statements to the House.
ITV and the BBC are working closely together on this and we welcome involvement from other broadcasters
Michael Jermey ITV
The Head of Sky News, John Ryley, said a TV debate offered politicians "a unique opportunity to re-engage a disillusioned electorate".
Mr Cameron said prime minister's questions was "no substitute for a proper primetime studio debate" and Mr Clegg said politicians had to find "new and different ways to engage with voters".
Sky political editor Adam Boulton denied the broadcaster had "broken ranks" with ITV and the BBC, which believed the channels were working together on getting a televised debate.
He said Sky would open a debate to other broadcasters to show live and said if there were a series of debates it would not expect to do all of them.
He said there would be a chair available for Gordon Brown "and we hope he occupies it".
The BBC's chief political adviser Ric Bailey said there had been lots of negotiations and "informal discussions", as securing a TV debate was a "delicate" process - with the best chance being for broadcasters to work together on a joint approach.
Steve Anderson, a former head of news and current affairs at ITV Network, was involved in efforts to secure a TV debate in 2001.
He said Tony Blair's media chief Alastair Campbell had advised the then-PM against taking part because his lead was "unassailable" and there was no need to do it.
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