Former News Of The World editor Andy Coulson has been detained on suspicion of committing perjury.
It relates to the trial of former Scottish politician Tommy Sheridan at the High Court in Glasgow in December 2010.
Mr Coulson, who gave evidence in the trial, was detained in London by Strathclyde officers and later taken to a Glasgow police station.
Police have 12 hours to question him before applying for a further 12 hour period if it is deemed necessary.
Former MSP Sheridan was jailed for three years in January 2011 after being found guilty of perjury during his 2006 defamation action against the News Of The World (NOTW) when Mr Coulson was editor.
Sheridan was awarded £200,000 in damages after winning the civil case.
But a jury at the High Court in Glasgow found him guilty of lying about the now-defunct tabloid's claims that he was an adulterer who visited a swingers' club.
The former Scottish Socialist Party (SSP) leader was released from jail in January after serving one year of his sentence.
Operation Rubicon detectives have been looking at whether certain witnesses lied to the court during Sheridan's trial as part of a "full" investigation into phone hacking in Scotland.
Mr Coulson, then employed by Downing Street as David Cameron's communications chief, told the trial in December 2010 he had no knowledge of illegal activities by reporters while he was editor of the NOTW.
Mr Coulson, 44, was detained last year in relation to Scotland Yard's long-running investigation into phone hacking at the paper.
He was held in July on suspicion of conspiring to intercept communications and corruption and had his bail extended earlier this month.