The Chancellor ended his 25-year membership of the Faculty of Advocates a week before Christmas.
Mr Darling, a respected lawyer prior to entering politics, gave no public explanation. However the Chancellor's exit followed a complaint to the Faculty by a member of the public about his House of Commons expenses for a second home.
During the summer scandal over MPs' expenses, it emerged that Mr Darling had 'flipped' his second home four times in four years and received tax advice paid for with public funds.
The 470-year-old Faculty of Advocates regulates the activity of around 700 members, both practising and non-practising and its code of conduct states that: 'An Advocate owes a duty not to bring the Faculty into disrepute'.
Mr Darling's spokesman described his boss's exit as a "coincidence". However, a legal source said:
“There was a complaint lodged by a member of the public about him flipping his house in Edinburgh. That automatically activated the disciplinary machinery. He’s learned about it and then decided he didn’t want the bad press and resigned. Once an advocate has resigned they are not capable of being disciplined. The spin from Number 11 Downing Street is that it’s because he hasn’t practised for a long time, but it was to avoid the embarrassment of the flipping scandal."I wonder if the Faculty will continue the investigation now that Mr Darling is no longer a member. His spokeswoman said: "There was absolutely nothing wrong in what he did about his houses. The disciplinary proceedings would not have been awkward and it is ridiculous to suggest he resigned because of this."