Prosecutors have ordered police to carry out a criminal investigation into allegations of perjury during Tommy Sheridan's defamation case.
Tommy Sheridan MSP represented himself during the defamation case
The Procurator Fiscal at Edinburgh has instructed Lothian and Borders Police to begin criminal investigations.
A Crown Office spokesman said it was not possible to speculate on the timescale for the investigation.
Mr Sheridan, who won his defamation action, dismissed the launch of the formal inquiry as "nothing new".
The former Scottish Socialist Party leader won his case against the News of the World newspaper in August after a four-week hearing at the Court of Session in Edinburgh.
Following the verdict, the News of the World described the jury's decision as "perverse".
It had accused the Glasgow MSP of cheating on his wife and taking part in orgies.
Eleven fellow members of the SSP told the trial that Mr Sheridan had admitted at a party meeting in 2004 that he had visited a swingers club in Manchester.
Four of Mr Sheridan's party colleagues backed his account of that discussion, insisting he had made no such admission.
The trial and its outcome led to public acrimony within the SSP which culminated with Mr Sheridan and another MSP, Rosemary Byrne, leaving to set up a breakaway left-wing party, Solidarity.
This weekend the News of the World made public a video recording by George McNeilage, who was Mr Sheridan's best man at his wedding. The newspaper claimed this showed Mr Sheridan admitting he had attended the Manchester club.
Mr Sheridan branded the story "a pack of lies" and declared: "A fictitious tape has been invented, concocted, and unleashed."
However, Euan McColm, the Scottish political editor of the News of the World, said: "The tape has been checked and verified by four leading voice analysts, all of whom agree that Tommy Sheridan is the man featured.
"Tommy Sheridan's claim that the tape is faked isn't credible."
On 22 August, the Crown Office said it had instructed the Edinburgh procurator fiscal to examine all of the evidence given in the defamation case to see if there were grounds for instructing a criminal investigation.
On Monday, a spokesman for the Crown Office said: "On the basis of information presently available to her the procurator fiscal at Edinburgh has instructed police to begin a criminal investigation into allegations of perjury.
"It is not possible to speculate as to any possible lines of inquiry.
"Lothian and Borders Police will submit a report to the procurator fiscal at Edinburgh in due course."
News Of The World Scottish editor Bob Bird said: "We welcome the police perjury investigation into the Tommy Sheridan case and will co-operate fully with the police inquiry."
Mr Sheridan said the Crown Office was "only doing its job".
"There's nothing extraordinary in what the Crown Office has done, they are only doing their job," he said.
"It is a rehashed announcement from six weeks ago, there's nothing new."
Mr Sheridan added that he would be happy to take part in any aspect of the police investigation.