DAVID Cameron's former spin doctor has hired a Scottish QC dubbed "the rottweiler" in his battle against criminal charges north of the Border.

Andy Coulson has opted for Richard Keen to fight his corner after the former News Of The World editor was charged in connection with evidence given during the Tommy Sheridan perjury case.

Ironically, Keen represented Sheridan until he was sacked by the left-winger.

Coulson, 45, was editor of the now-defunct Murdoch tabloid between 2003 and 2007, after which he took up a role working for Cameron.

When Cameron became Prime Minister in 2010, Coulson held the role of his communications director until his resignation in January 2011 amid pressure surrounding the phone-hacking scandal.

During his period in Government, Coulson was called by Sheridan to give evidence in his perjury trial.

Sheridan had been charged with telling lies in an earlier defamation case against the owners of the News Of The World.

Although Sheridan was found guilty of perjury, Strathclyde Police launched an investigation into the evidence given by some of the witnesses at the trial.

Coulson was subsequently detained and charged with perjury last May.

It is believed Coulson originally intended to hire the late Paul McBride as his QC.

The Sunday Herald can now reveal that Coulson's solicitor, Paul Kavanagh, has instructed Keen.

In an illustrious career, Keen has worked on the Piper Alpha case and led the defence of Lamin Fhimah in the Lockerbie bombing trial.

More recently, he also acted for the Weir Group plc in the case involving the United Nations sanctions in Iraq

Keen is also Dean of the Faculty of Advocates.

One legal source said: "He is a brilliant lawyer."

However, a low point was being dismissed by Sheridan during the initial defamation case.

Keen represented the former Glasgow MSP in the first week, but commitments in the House of Lords meant that he could not be in court every day.

A mistake by Keen's junior counsel prompted Sheridan to withdraw instructions from the whole team.

Despite the clash, Sheridan tried to rehire Keen after he won the defamation case.

Speaking to the Sunday Herald in 2007, Keen said: "It is true that an approach by his solicitors was made. I didn't believe it was professionally appropriate to take up the case."

On the decision to dispense with his services, Keen said: "Tommy Sheridan and his advisers took a very political move and it worked very well for him."

Although Coulson was charged nearly a year ago, it is not clear when the Crown Office will make a final decision on the case.

Coulson has also been charged by authorities south of the Border with conspiring to hack phones.

Contacted last week about the situation, Keen said: "I can't make any comment."