London: Andy Coulson, the British Prime Minister`s former communications director and one of the central figures in the phone hacking scandal, is being investigated for allegedly committing perjury while working for David Cameron in Downing Street.

The police in Scotland said they had opened a perjury inquiry centred on evidence Coulson gave in court last year that led to Tommy Sheridan, former Member of the Scottish Parliament, being jailed.

Coulson was a major witness in the trial involving Sheridan, who was accused of lying in court when winning a libel action against the News of the World. Coulson had been the editor of the Sunday tabloid when it ran a story accusing Sheridan of being an adulterer who visited swingers` clubs.

At the trial Coulson denied knowing that the paper paid corrupt police officers for tip-offs, which contradicts recent disclosures that News International has uncovered emails showing payments were made to the police during his editorship.

Coulson told the court in December 2010 that he had no knowledge of illegal activities by reporters while he was editor of the newspaper.

He also claimed: "I don`t accept there was a culture of phone hacking at the News of the World".

Strathclyde police`s assistant chief constable, George Hamilton, told The Guardian: "Following our discussions with the crown, we have now been instructed to carry out a full investigation into allegations that witnesses gave perjured evidence in the trial of Tommy Sheridan and into alleged breaches of data protection and phone hacking".

PTI