Alex Salmond has returned to the 1970s in the war over an independent Scotland’s finances by laying down the marker: “It’s our oil.”
It came as it emerged an internal report into projected oil prices will be published imminently, leading to accusations from opposition parties that the Scottish Government was trying to “cook the books”.
The SNP has come under fire after a secret document emerged admitting oil prices were “volatile”.
A Government spokesman confirmed the report is due to be published soon but could not confirm when it would emerge.
He also said the official Office for Budget Responsibility (OBR) figures were low compared to other outlets.
The spokesman said: “OBR figures are substantially below other projections. Clearly the OBR figures are some way out from other UK and outside agencies.
“We will have more to say about projected oil revenues in the coming years very, very soon.”
The spokesman confirmed the decision to bring forward the new document predated the emergence of finance secretary John Swinney’s report and that an internal investigation has been launched into the source of the leak.
Labour’s North East MSP Richard Baker accused the SNP of being “embarrassed that the truth about independence in their own words has become public.”
He also claimed the Government was prepared to say “one thing in private then cook the books for the public”.
Alex Salmond had earlier clashed with opposition leaders over the leaked document during a raucous First Minister’s Questions, which included presiding officer Tricia Marwick taking the rare step of banging her gavel to restore order.
Ms Lamont claimed the leaked paper shows that SNP ministers “say one thing in private” but that they “deny in public the truth we all know” and Mr Swinney is “talking to the cabinet about cutting” services.
Mr Salmond retorted by saying the document highlights “real-terms growth in public spending” in the future and said oil would form the base for such policies.
He said: “Every other society across Europe would be crying out for that sort of natural resource. Is it not time for us to match the great natural and people resources of Scotland and build a society of which every one of us can be proud?”
Arriving in the chamber after proceedings had started, Mr Swinney was cheered and applauded by all parties sarcastically by the opposition as a brief reshuffle took place on the SNP benches.
Dundee East MSP Shona Robison vacated her seat for Mr Swinney to settle on the front bench, while she in turn forced local government minister Derek Mackay to the backbenches.
Scottish Conservative leader Ruth Davidson demanded Mr Salmond publish an update to the “private” document to set out the Government’s position.
Mr Salmond replied: “For 40 years we’ve had Tory politicians telling us that North Sea oil and gas is running out. We now have the evidence that the next 40 years will have greater value than the last.
“What we’re going to make sure is, having London had its turn for the last 40 years, the next 40 years will be Scotland’s turn.”