It didn't take long for the backbiting to begin after this week's TV debate.

On Thursday morning, the front page of the Labour-supporting Daily Record carried damaging quotes from a "senior SNP figure" about Alex Salmond's performance.

"There is a good case to be made on currency, but Salmond did not make it. He is First Minister, he has been preparing for years ... it did not go well," said the anonymous source. The Holyrood rumour mill swiftly attributed the comments to one of Nicola Sturgeon's advisers.

Labour's Johann Lamont used the story to unsettle Salmond and his deputy at First Minister's Questions when she joked: "I do not know what Nicola Sturgeon made of that answer [to a question put to the First Minister] but I dare say I will read what she thought from an unnamed source in tomorrow's papers."

However, the SNP's reputation for iron discipline at Holyrood is well deserved.

It seems highly unlikely, on the basis of one sub-par debate performance, and barely a month away from their life-long goal of a Yes vote, that the party's MSPs will start panicking. Yet the currency issue does have the potential to divide the wider Yes campaign, because it has always been a faultline through the camp.

The SNP is isolated in the Yes camp in wanting to give up some of an independent Scotland's putative sovereignty to share the pound.

The Scottish Greens, Scottish Socialists, and even Yes Scotland's chairman Dennis Canavan would all prefer that Scotland instead establish its own new currency.

This attracted some adverse comment at the start of Yes Scotland, but the movement was able to spin the division as evidence of the all-inclusive nature of the Yes campaign.

But the divisions did not go away, and now they're becoming inflamed once again.

Salmond's claim that the sovereign will of the people equates solely to his plan for currency union despite many of his Yes colleagues wanting a Scottish currency will not help.

Jim Sillars, the ex-SNP deputy whose "stupidity on stilts" verdict on a currency union was quoted approvingly by Darling on Tuesday, wasted no time in telling the BBC where he stood.

"Plan B, separate Scottish currency, perfectly normal answer. It happens all over the world, why shouldn't we do it?" he asked.

Former SNP leader Gordon Wilson, a frequent collaborator of Sillars and a fellow Salmond critic, also chipped in promptly.

The First Minister's position was "too simplistic", given Westminster's ruthlessness, he said in an article issued on Friday.

"It was sustainable until the big debate between Salmond and Darling when the audience reaction showed that bold assertions were not enough ... references to Fiscal Commissions and Nobel laureates are meaningless to most folk."

Wilson argued London would agree a currency union for fear of harming the rUK economy, but added that Scotland could always use the pound in an informal way - known as sterlingisation - and then ultimately establish a new currency.

"He [Salmond] does not have to abandon his first preference of using the pound" he said.

"He needs to explain the options simply," he added.

A couple of years ago, this kind of advice could be brushed aside as of little import.

But with the First Minister unable to name a Plan B in case he is accused of panic, and every angle of the debate magnified in the closing stages, it is deeply awkward for him.

The biggest problems in politics often come from within.