The man trying to keep Scotland British

In contrast, Darling used it to issue a call to arms in defence of the Union between Scotland and England. The Scottish government is planning to hold a referendum on independence in Autumn 2014.

Former Scottish Labour leader Iain Gray told Al Jazeera that Darling is the perfect man to convince Scots to stick with the Union.

"Alistair has a reputation for being unflappable, and that is well-deserved. The banking crisis demonstrated that the hairier the situation, the cooler he gets."

Gray has known him all his adult life and was Darling's special adviser in the Scottish Office. "As a minister, too, he was brilliant at getting the best out of everyone he worked with," he continued. "That will stand him in good stead in a cross-party campaign - not just keeping it together, but keeping it focused on the shared objective."

Senior sources within the Labour Party describe him as a "classic Edinburgh lawyer" who knows how to handle his brief and gets the job done. In some ways, leading the cross-party "No" campaign is a job that he was born for. His grandfather was a Liberal candidate, and his great uncle, Sir William Darling, was a Conservative MP and Lord Provost of Edinburgh.

Little wonder, then, that he was marked out as a future political star at an early age.

Alistair Darling entered parliament in 1987 as the MP for Edinburgh Central, winning the seat from the Conservatives. This was a watershed election in Scotland. Conservative Prime Minister Margaret Thatcher was at the height of her powers, exuding the purpose and authority of a dreadnought. But while she returned to Downing Street with a huge majority based on support from voters in England, her appeal didn't travel north of the border. The number of Scottish Tory MPs fell from 21 to ten.

Since then, the Tories have sunk even further in Scotland - and now have just a single MP; it has become a standing joke that he is outnumbered by the two giant pandas in Edinburgh Zoo.

Within a year of his election, Darling was appointed to the front bench and he is one of only three ministers who served in the cabinet throughout the whole of Labour's 13 years in office from 1997 to 2010.

He developed a reputation for handling tricky briefs, such as Social Security and Transport, and taking them out of the headlines. His success earned him the title of "Britain's most boring politician" two years in a row.

In a reference to his distinctive appearance, one senior member of the Labour Party in Edinburgh memorably describes him as "a real safe pair of eyebrows". Darling got his reward when Gordon Brown became prime minister and put him in charge of the Treasury. By then, he was typecast, and the right-leaning Daily Mail dismissed his first budget, in 2008, as "pulverisingly boring".

Darling admits in his account of his time as chancellor that even his own mother fell asleep in parliament's public gallery.

People might have paid more attention if they had any inkling of the financial crisis that was about to unfold. One of Alistair Darling's favourite phrases is "expect the worst and you won't be let down".

He threw off his reputation for dreich Edinburgh dullness in an interview with The Guardian, in which he warned the public that the nation was about to face the deepest and most serious financial crisis of the 20th century.

Speaking at his family croft on the staunchly Presbyterian Isle of Lewis, he said: "The economic times we are facing… are arguably the worst they've been in 60 years. And I think it's going to be more profound and long-lasting than people thought."

His warning provoked a furious reaction from the prime minister's aides, who accused him of undermining the economy. Darling says the "forces of hell were unleashed" against him, but he turned out to be right.

On a wet Tuesday morning, on October 11, 2008, he received a phone call warning that the Royal Bank of Scotland would collapse within hours. What was he going to do about it? In the most extraordinary day in British banking history, Darling agreed to pump £37bn ($58bn) into the Royal Bank of Scotland, Lloyds TSB and HBOS.

Catherine MacLeod is a close family friend who worked with him at the Treasury. She said: "He was absolutely the right person to be there as the economic crisis unfolded. It would have been easy to panic, but he did not flinch." She added that his steadiness and collegiate manner won him the respect of officials. Nobody has ever heard Alistair Darling shout or raise his voice, it would seem.

British banks are back in the headlines this week, with Barclay's chief executive, Bob Diamond, resigning following allegations that his bank manipulated Libor and Euribor interbank lending rates. As chancellor at the time, questions are being asked about how much Darling knew about what was going on at the bank.

Nevertheless, the prime minister, David Cameron, is relying on him to set out the case for Britain. With such little support for Conservatives, he doesn't have the credibility to do the job himself - and sometimes looks like the representative of a foreign power on his visits north of the border.

MacLeod sees this as a case of "cometh the hour, cometh the man".

Senior figures in the "No" campaign believe that Darling's status as a former UK chancellor and his reputation for straight talking are significant political assets. He has an intellectual disdain for Scottish nationalism, and is disparaging about what he says is a lack of detail on questions such as the currency that would be used in an independent Scotland.

But this is a cause that runs deep with him, and he also rejects Scottish independence in his heart aswell as his head. Darling is an authentic representative of the old Edinburgh establishment and, if you listen carefully, you can hear the voice of his great-uncle whispering down the generations.