Public assets sold off by the Conservative government face being renationalised with "no compensation" by Jeremy Corbyn if they go for a knockdown price, the left-winger's campaign revealed.
Royal Bank of Scotland is among the state-backed resources the MP would "reserve the right" to take back into public ownership if he leads the Labour party.
The process could happen "with either no compensation or with any undervaluation deducted from any compensation for renationalisation" if they are disposed too cheaply over the next five years, according to the Observer.
It comes as a former Bank of England adviser was among more than 40 economists publicly to back the Islington North MP's policies in a significant boost to his Labour leadership campaign.
Danny Blanchflower, a former member of the monetary policy committee, is among the signatories to a letter in the Observer dismissing claims the MP is "extreme", arguing instead that his opposition to austerity is "actually mainstream economics".
The letter said: "The accusation is widely made that Jeremy Corbyn and his supporters have moved to the extreme left on economic policy. But this is not supported by the candidate's statements or policies. His opposition to austerity is actually mainstream economics, even backed by the conservative IMF. He aims to boost growth and prosperity."
But leadership rival Andy Burnham said Labour must show voters it is "serious" on the economy and warned that "economic credibility is all".
Earlier, the shadow health secretary warned against flirting with quitting the European Union in an apparent swipe at rival Mr Corbyn.
Insisting a British exit would put jobs and the economy at risk, the shadow health secretary said it was time to "nail our colours firmly to the mast" and pledged to be "proudly pro-European" if he takes the top job.
The warning comes after Mr Corbyn suggested Labour could hold a special conference before deciding its response when Prime Minister David Cameron puts forward his package of reforms on Britain's relationship with Brussels ahead of the in/out referendum.
At a campaigning event in Swansea, Mr Burnham said: "In just over a year, Britain faces a momentous decision that will affect every single person in our country; a decision that will define our politics and our country for the rest of this century.
"The stakes couldn't be higher and this is no time for equivocation. To flirt with exit from the EU is to put people's jobs, communities and future prosperity at risk. This is no time to cut ourselves off from our largest market. It is time to nail our colours firmly to the mast."