Alex Salmond (pictured, Reuters) has said there would be an "inevitable investigation" over allegations that the Treasury leaked "market-sensitive" information about Royal Bank of Scotland's proposal to register itself in England if Scotland votes for independence.
The First Minister and SNP leader said the alleged BBC briefing by a "Treasury source" was "a matter of extraordinary gravity", and urged the BBC to co-operate with the probe that must follow.
Speaking at a press conference for international journalists in Edinburgh, Salmond said: "A Treasury source told the BBC that it had discussed the plans with RBS.
"The Treasury, officials or ministers, are not allowed to brief market-sensitive information.
"Market-sensitive information, and it's a basic rule, cannot be released prior to the market announcement at 7am this morning.
"RBS share price changed overnight. This is a matter of extraordinary gravity.
"I've always respected, and I will continue to respect, the journalistic right to maintain and protect sources.
"But I know that the BBC will want to co-operate with the inevitable investigation by the Cabinet Secretary to the briefing of this information, given that the briefing of information – even if we weren't in a referendum campaign, even if there weren't purdah rules which are meant to apply to government – the briefing of market information is as serious a matter as you can possibly get."
Some members of the audience – which was packed with supporters as well as international journalists – laughed and applauded when the First Minister spoke of the BBC's "impartial role as public sector broadcaster".
BBC political editor Nick Robinson was also heckled from the audience while questioning the First Minister.
RBS, which has been based in Scotland since 1727, said it would be necessary to re-domicile the bank's holding company and its main operating entity to England if Scotland votes Yes.
It said the decision to re-domicile should have no impact on everyday banking services and it would retain a significant level of its operations and employment in Scotland.