Salmond has met his nemesis in Darling

Mr Wishart's intemperate intervention was par for the course. Mr Salmond should have known better. He had a ringside seat for much of Mr Darling's parliamentary career. They joined the House of Commons on the same day in June 1987. Mr Darling confounded expectations even then. He wasn't expected to win Edinburgh Central (Robin Cook had upped sticks to the safer seat of Livingston) and at the last General Election, after four difficult years at the Treasury, he was one of the few Labour MPs in the UK to increase his majority.

From 1988 until 2010 Mr Darling did not leave the front bench. He earned his spurs battling the Tories, Liberal Democrats and the SNP in and out of Parliament for 10 years before Labour's landslide victory in 1997. He was variously Secretary of State for Transport, Work and Pensions, Social Security, Scotland, Trade and Industry, as well as Chief Secretary to the Treasury and eventually Chancellor the Exchequer, the second most important office in Government. He saw off all comers and, as is the way in politics, there were many ready to step into his shoes.

The House of Commons is a bear pit. Mr Darling survived for 25 years not least during the global banking crisis when he retraced his steps from Downing Street to Westminster more often than he'd care to remember to give yet another explanation of the latest twists and turns in the crisis, and it was never good news. He was held to account by select committees, he regularly made the Government's case in the European Union, he argued the UK's position around the world at G8 and G20 summits and he held his own whether he was speaking at the TUC or CBI.

Often he did not relish the prospect of another foray into the public domain but he understood this was part of the job. Mr Darling had learned his trade at the Scottish Bar, amongst some of the most articulate, eloquent, hard-nosed and entertaining advocates in Scotland. And when he wasn't at work he was fighting his corner in the corridors of Lothian Regional Council, where he was once chairman of the transport committee.

He was never going to be fazed by the prospect of facing Alex Salmond. Mr Salmond was not a noted parliamentary performer, although he was sent from the chamber and dismissed for a week for verbally attacking Nigel Lawson during a budget speech. The House of Commons is a strange place in which politicians on all sides respect worthwhile contributions. No-one ever flocked into the House of Commons to be entertained by Mr Darling, he never tried to play it for laughs but they did give him a hearing because they knew he would treat them with respect and have a thoughtful and considered contribution to make.

And so it was at the referendum debate. While Mr Salmond wanted to talk about aliens and driving on the wrong side of the road Mr Darling was serious. He wanted to know how we would pay our bills if Scotland could not join a currency union.

Mr Salmond should not have been surprised by Mr Darling's line of questioning. He has been asking the same question ever since the UK parties ruled out the possibility of a currency union. What was surprising was Mr Salmond's inability to answer. Had he not thought about it? Was he not telling? Did he not know? Take your pick. And when Mr Salmond insisted there would be a currency union because he knew what was best for England, Wales and Northern Ireland, his credibility was blown out of the water. The First Minister can speak for Scotland. His writ runs no further.

Expectation management matters. Mr Salmond's name will be associated with the biggest mismanagement of expectations since Ally MacLeod raised Scotland's hopes before their dismal performance in the 1978 World Cup.

Catherine MacLeod is a former political editor of The Herald and was a special adviser to Alistair Darling when he was Chancellor of the Exchequer.