The First Minister’s chauffeur, a former Metropolitan police officer, is carrying out “risk assessment” duties on official visits.

Roger Cherry was put on a higher pay grade in 2008 and relocated to accommodation in the North East of Scotland to be close to Mr Salmond’s home.

The criticisms come after PCS, the largest civil service union, repeatedly queried the First Minister’s transport arrangements.

It is understood Mr Cherry was one of Mr Salmond’s regular drivers in the Scottish Government car service (SGCS) until July 2008, when he was made Mr Salmond’s personal chauffeur.

Civil servants believed his move north was necessary for Mr Cherry, who used to live close to the capital, to avoid disruption to his weekend.

The move also resulted in Mr Cherry’s pay being raised in November 2008.

Since January last year, PCS has asked the Government for answers to a series of questions about Mr Cherry’s relocation and a copy of the business case that supported it. The union is also asking for details of the extra duties Mr Cherry performs, which were part of the promotion, and has requested a meeting since March to discuss the case.

PCS intervened after other chauffeurs in the SGCS complained about not being able to apply for the new post.

A senior government source confirmed that one of Mr Cherry’s “additional responsibilities” was undertaking risk assessment at events for Mr Salmond -- making him the First Minister’s unofficial bodyguard.

Although classed as a driver, Mr Cherry routinely leaves his car to accompany the First Minister at official events, using his police training to watch for potential trouble. In one week in November, he was filmed following Mr Salmond round a new civic centre in West Lothian and joining him in a torchlit procession in East Lothian.

At the second event, he stayed at the First Minister’s shoulder.

Mr Salmond has become more security conscious since becoming First Minister. In 2008, the SNP increased spending on security at conferences more than five-fold, from £2,554 in 2007 to £13,934, with the First Minister being swept into Perth Concert Hall surrounded by bouncers.

It is understood there has been a debate inside the Government on whether the public purse should pay for Mr Salmond’s personal security.

Mr Salmond is reluctant to have a formal police presence at official events, so has settled for a less high-profile arrangement with Mr Cherry.

Labour election and campaign manager, John Park MSP, said the First Minister had to give a full account of his driver’s promotion and relocation package.

He said: “This is typical of Alex Salmond’s delusions of grandeur. That he is riding roughshod over proper procedures with a special driver and bodyguard for himself is no surprise. Maybe because of all his broken promises he is a bit paranoid and feels he needs a bodyguard, but this all a bit ridiculous.”

Mr Salmond has been at the centre of a series of rows over the use of public funds. More than £100,000 was spent on six meetings of his Council of Economic Advisers and he has used Edinburgh Castle for functions three times as often as his predecessor Jack McConnell.

A Scottish Government spokesman said: “Mr Cherry’s relocation... makes eminent sense in terms of efficiency and cost-effectiveness.”