The Chief Secretary to the Treasury condemned as "absolutely outrageous" the Scottish Finance Secretary's repeated refusal to say how much establishing a new state would cost while at the same time setting up transition teams to manage the creation of an independent Scotland should voters say Yes in September.
Mr Alexander forcefully defended the UK Government's policy presentation against the pro-independence campaign's charge of scaremongering, describing it as "balanced", including the use of Lego figures to show what the £1,400 Union Dividend would buy, such as 280 hotdogs at the Edinburgh Festival.
"There was a colossal sense of humour failure over that," he said. "God knows what Scotland would be like if all these po-faced Nationalists were in charge of an independent Scotland; there would never be a joke told anywhere. We need to lighten up a wee bit."
In an interview with The Herald for the latest Scotland Decides supplement published tomorrow, the Liberal Democrat Highland MP also said:
lan independent Scotland getting a geographic share of North Sea oil and gas revenue was a reasonable working assumption but would have to be "part of the negotiations"
lthe SNP Government's estimates of future oil revenue were "fantastical projections"
lAlex Salmond's assertion that, should Scotland become independent, England would not be a foreign country was "legally illiterate" and
lthe UK had been a "beacon" to the world in breaking down barriers between countries and indep-endence would be a "fundamentally" backward-looking step".
Mr Alexander refused to say whether or not the Coalition had apologised to Professor Patrick Dunleavy from the London School of Economics, who claimed his research on independence set-up costs had been misused by the Treasury.
He suggested the row over the UK Government's promotion of its £1.5bn estimate for establishing an independent state had exposed a big hole in the Scottish Government's prospectus.
"It drew out something very important, which was the people who want to set up a new state are unwilling to reveal to the people of Scotland how that would be done and how much it would cost. It's an utterly extraordinary state of affairs. To hear John Swinney on Radio Scotland doing his Michael Howard moment when he was asked 13 times (and did not give a figure) was an extraordinary thing."
Asked what he made of Prof Dunleavy's £250m estimate for the set-up costs, which the First Minister described as "reasonable", the Chief Secretary said: "This would build a bridge about a quarter the way across the Forth. It's not plausible."
He said the simplest way to resolve the argument would be for Mr Swinney to publish a figure for set-up costs.