Downing Street has ordered an inquiry to find the Coalition minister who went dramatically off-message by contradicting Chancellor George Osborne's insistence that sharing the currency with an independent Scotland had been completely ruled out.
A Westminster Government aide said yesterday: "Of course we want to know who said this but more important than finding the name was getting the message out there that he was entirely wrong."
Friday's revelation from the unnamed figure that the SNP's plans for a currency union would "of course" be negotiated sent the Better Together campaign against independence into a tailspin.
He or she had admitted that refusing to let Scotland share sterling was a negotiating tactic which would be discarded in the event of a Yes vote.
It followed an ICM poll that provided further evidence of the gap narrowing between the No and Yes camp in the run-up to the referendum on September 18.
The survey also revealed the majority of Scots thought the dire warning by Chancellor George Osborne and his Labour and Liberal Democrat counterparts that the pound could not be shared was a bluff.
Hours before the unnamed minister's comments emerged, Deputy Prime Minister Nick Clegg seemed irritated at the LibDem conference in Aberdeen when told former chief executive Andy Myles and former treasurer Denis Robertson Sullivan had come out for a Yes vote.
Asked if First Minister Alex Salmond's vision of sharing things such as the currency chimed with federalists, Mr Clegg insisted there would never be a currency union.
He said Mr Myles and Mr Sullivan were wrong, the words of the First Minister could not be trusted, and likened Mr Salmond to a flat-earther who believed the moon was made of cheese.
Chief Secretary to the Treasury Danny Alexander was also vehement on the currency question.
But unease and concern erupted at a fringe meeting when former Libdem Scottish leader Tavish Scott was highly critical of Better Together for failing to make full use Labour's "big beasts" with wider appeal to party grassroots than Alistair Darling.
A regular meeting of Better Together on Friday was billed in some quarters as a crisis summit, but things were to get much worse.At a meal with journalists at an Italian restaurant in Aberdeen mobile phones began to ring.
Soon Scottish Secretary Alistair Carmichael had to deny the unnamed minister's claim that there would be a currency union in the event of a Yes vote.
"Project Fear has become Project Laughing Stock," as one gleeful Nationalist put it.
Meanwhile Mr Carmichael said Better Together needed to match the nationalists' hunger for victory.
The Liberal Democrat MP warned Scotland could end up voting for independence if those in favour of remaining part of the UK left it too late to make their voices heard.
He said yesterday: "It is eminently possible that they will be able to buy momentum with the advertising and campaign resource they have. We're never going to match them for the spend, but in terms of the hunger I think we have to match them for just how badly we want this.
"That is always going to be a challenge, because for nationalists this is the issue that defines them, whereas for a Labour supporter, a Liberal or a Conservative, this can be an issue you care about but is not one that defines you."
lAlmost half - 48% - of small business owners in Scotland think independence would be bad for their company, a new survey suggested. Ingenious Britain, which polled 1000 bosses, found 37% said leaving the UK would be positive.