Former SNP deputy leader Jim Sillars has attacked "scaremongering" business leaders, warning they will face a "day of reckoning" if Scotland votes Yes next week.
Mr Sillars accused large companies and banks of "subverting Scotland's democratic process" by making high-profile interventions in the independence referendum debate.
Oil giant BP would face nationalisation in an independent Scotland while bankers' "casino days" would be over, Mr Sillars said.
The Yes campaigner revealed he had planned to retire following the vote next Thursday but would instead be "staying in".
Mr Sillars was speaking on the campaign trail in Edinburgh's Wester Hailes area from his Margo Mobile, set up in memory of his late wife Margo MacDonald MSP.
He said: "This referendum is about power, and when we get a Yes majority we will use that power for a day of reckoning with BP and the banks.
"The heads of these companies are rich men, in cahoots with a rich English Tory Prime Minister, to keep Scotland's poor poorer through lies and distortions. The power they have now to subvert our democracy will come to an end with a Yes.
"BP, in an independent Scotland, will need to learn the meaning of nationalisation, in part or in whole, as it has in other countries who have not been as soft as we have been forced to be.
"As for the bankers: your casino days, rescued by socialisation of your liabilities while you waltz off with the profits, will be over."
Mr Sillars added: "What kind of people do these companies think we are? They will find out."
His comments were seized on as "threats" by campaigners for a No vote.
Scottish Conservative finance spokesman Gavin Brown said: "It seems the Yes campaign are completely losing the plot.
"To even suggest BP would need to learn the 'meaning of nationalisation' and there will be a 'day of reckoning' for big businesses is not only threatening but also utterly unnecessary.
"Whether Scotland becomes independent or not, we would need big businesses to bring in investment and help create jobs.
"The Yes side are playing a dangerous game by attacking global companies just because they have dared to question the SNP's fantasy economics."
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