Danny Alexander: strait-laced loyalist who played a key role in coalition negotiations

Danny Alexander is rewarded for his commitment

His lack of experience in the finer principles of economics has made Danny Alexander's promotion to the post of Chief Secretary to the Treasury a surprising one. Yet after the previous incumbent survived just 18 days, Nick Clegg and David Cameron were hoping the man from the Highlands would bring another quality to the role – a distinct lack of excitement.

Even before his arrival at Westminster, during his time as the director of communications for a pro-European group, he earned a serious, straight-laced reputation. In the early hours of one party conference, while most journalists and MPs had long-since abandoned their professional roles in favour of a drink and a gossip, Mr Alexander continued to prowl the bar, seeking to persuade those present of the merits of a single currency.

But his commitment to his chosen causes is precisely why he has become so trusted by Mr Clegg, the Deputy Prime Minister. After entering parliament in 2005, Mr Alexander gave up his role as the party's spokesman on Work and Pensions in June 2008 to concentrate on his job as the Lib Dem leader's chief of staff. He was also handed the responsibility of drafting the party's manifesto for the 2010 election.

His unswerving loyalty perhaps explains why Mr Clegg felt so able to divulge his innermost thoughts about the capabilities of his own shadow Cabinet team to Mr Alexander during a flight to London. While Mr Clegg criticised the likes of Chris Huhne and Steve Webb during the conversation, overheard by a newspaper reporter, Mr Alexander was left in no doubt about the abilities of Mr Laws, whose shoes he now has to fill. "He's got a forensic intelligence," Mr Clegg told him. "He's probably the best brain we have."

He will be well aware that Mr Clegg's support won't protect him from accusations that he is too young and too inexperienced in the Treasury brief to replace Mr Laws. He turned 38 just weeks ago, and was already struggling to keep on top of his job as Scottish Secretary following the birth of his second child. In fact, his unlikely promotion marks one of the most meteoric rises in recent Westminster history. Just five years ago, before picking up his Inverness, Nairn, Badenoch and Strathspey seat, he was head of communications for the Cairngorms National Park. He had started his career as a regional press officer for the Liberal Democrats, before taking communication roles with the Brussels think tank, the European Movement, and the pro-euro campaign, Britain In Europe.

The brilliance of his predecessor is not just a problem for Mr Alexander.

It has also caused a headache for Mr Cameron in keeping his own backbenchers onside. Some Tories, bowled over by Mr Laws' performance in the Commons last week, were last night grumbling that Mr Alexander would struggle in the role, with his only financial grounding coming from his brief time studying Philosophy, Politics and Economics at Oxford. Unlike Mr Laws, Vince Cable or Mr Huhne, he does not have any experience in the City.

Some Tories are also concerned about his pro-euro credentials. One Europhile, the Justice Secretary Ken Clarke, has already revealed his delight at having an ally at the heart of the Treasury. The pair met during Mr Alexander's time campaigning for a single currency. The markets may fear that the coalition has lost not only an impressive performer but also the lynchpin of the Tory/Liberal Democrat agreement. Mr Laws had come close to joining the Tories and had been asked to defect from the Liberal Democrats by George Osborne while the Tories were in opposition. With him gone, the danger is that the join between the two parties will become ever clearer.

But discounting Mr Alexander may be unfair. He impressed senior Tories for his role in negotiating the coalition contract, which he drew up with the Tory manifesto chief, Oliver Letwin. Even before his second promotion in less than a month, he had already been given seats on eight highly influential Cabinet committees, including the "coalition committee" in which disagreements will be hammered out, and the committees covering economic affairs and banking reform.

Despite his apparent straight bat, it has not taken long for Mr Alexander to become the target of renewed media interest. Before last night, his only expenses war story was a claim for a 99p for a bottle of Mr Muscle glass cleaner. But the Telegraph has now accused him of using a loophole for avoiding paying capital gains tax on his second home in London. "I sold the flat in 2007 and moved to another flat but was advised that CGT was not payable," he said. Cabinet colleagues will be hoping it is the last nasty surprise.