Leaders would relish the chance of head-to-head television debate

It came after a spokeswoman for the Prime Minister flagged up the idea, but later on flagged it down.

The spokeswoman initially said that while there were at present no plans for a PM/FM encounter before the TV cameras, she added: "It is something we will have to take back and consider."

In response, Alex Salmond eagerly told reporters that he would relish the chance of locking horns with Mr Cameron on the issue of independence, saying: "That would be hugely appropriate. I'm sure there will be a range of debates but I would be delighted to debate with the Prime Minister. I'll do it now, next week, any time up to the vote in the autumn of 2014."

A spokesman for the First Minister also told The Herald: "In principle, the First Minister is always keen to debate with opponents and there is absolutely no reason to expect this will be any different now, quite the contrary when we are making the case for an independent Scotland."

But Margaret Curran, the Shadow Scottish Secretary, said she feared it would personalise such an important issue, adding: "This should not be about two self-important men but the people of Scotland."

The Coalition Government then appeared to step back, with one senior source suggesting a key head-to-head between the Prime Minister and First Minister was "highly unlikely" and stressing that the debate was primarily for Scottish politicians in Scotland.

It might be that the pro-UK strategists fear having an English Tory defending the Union would simply do more harm than good.

Scottish Secretary Michael Moore, when asked about the prospect of a televised clash of the heavyweights, said: "These matters are going to be discussed and sorted out between the campaigns and the broadcasters.

"There are going to be lots of debates over the next couple of years. The Prime Minister rightly said this was a debate that should be led by and feature people in Scotland."

He added: "It's a slightly curious decision that the First Minister might choose to debate the future of Scotland with somebody from outside Scotland, but there is going to be no shortage of opportunity for that debate."

One senior producer at STV, which screened live debates in the run-up to the last Scottish election, said: "It's safe to say there will be lots of set-piece debates.

"We have had some initial thoughts here and are discussing it within the station. We'll be speaking to both sides."

He added: "The eyes of the world will be on Scotland and these debates could be more significant than in the run-up to the 1997 referendum when the result was a foregone conclusion."

A spokesman for BBC Scotland would only say: "Programming details will be released as they are finalised."

A spokesman for the Yes Scotland campaign said: "This is for the FM and PM to decide. We welcome all healthy debates on the benefits of independence."

The Better Together Campaign also made it clear this was a debate to be had by Scottish politicians and stressed it was not sure a TV head-to-head between Mr Cameron and Mr Salmond would ever take place.

However, a spokesman said the No campaign would welcome such an encounter between its leader Alistair Darling and the First Minister.

After the last General Election, when the media and many voters became enthralled by the TV debates involving Mr Cameron, Nick Clegg and Gordon Brown, the on-camera clashes have now become an accepted staple of political debate.

The first of the US presidential election TV debates – screened to tens of millions of Americans – re-invigorated Republican Mitt Romney's flagging campaign at the expense of the Democrats after his strong performance contrasted with President Barack Obama's lacklustre showing.

l A Comres online poll for ITV News at Ten showed 58% of British adults and 55% of Scottish adults believed Scotland's economy would suffer if the nation became independent. Of the 2100 adults polled, only 175 were north of the Border.