Alex Salmond claims Danny Alexander has been "caught red-handed" with "scaremongering" claims about the impact of Scottish independence.
The SNP leader told the BBC the Treasury's calculations had been "blown to smithereens" by the same academic whose work underpins the British Government's analysis.
Professor Patrick Dunleavy of the London School of Economics said Treasury figures about the cost of setting up a new independent government were "bizarrely inaccurate".
Mr Salmond seized on Professor Dunleavy's words, saying: "We have the Chief Secretary to the Treasury left with no credibility whatsoever. He’s been caught red-handed engaged in a scaremongering campaign.”
More top news
A man who was abused by John Allen as a child has spoken out as the former care home boss has been found guilty of a further eight charges.
A 101-year-old retired teacher has started a new hobby, giving inspirational talks to struggling young jobseekers.
Cloud cover will keep temperatures overnight a little warmer than usual for this time of year. Expect some mist and fog by morning.