Prime Minister David Cameron's former communications chief, Andy Coulson, has been detained on suspicion of committing perjury during the trial of former MSP Tommy Sheridan.
The 44-year-old was detained in London this morning by officers from Strathclyde Police.
Coulson gave evidence in Mr Sheridan's perjury trial at the High Court in Glasgow in December 2010.
He was also arrested last year in relation to Scotland Yard's long-running investigation into phone-hacking at the News of the World.
He was held in July on suspicion of conspiring to intercept communications and corruption and had his bail extended earlier this month.
A Strathclyde Police spokesman said: "Officers from Strathclyde Police Operation Rubicon detained a 44-year-old man in London this morning under section 14 of the Criminal Procedures Scotland Act on suspicion of committing perjury before the High Court in Glasgow.
"It would be inappropriate to comment any further at this time."
It is understood Coulson is on his way to Glasgow.
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 director of communications, told the trial in December 2010 he had no knowledge of illegal activities by reporters while he was editor of the News of the World.
He also claimed: "I don't accept there was a culture of phone hacking at the News of the World."
Sheridan was ultimately jailed for three years in January 2011 after being found guilty of perjury during his 2006 defamation action against the News of the World.
He 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 MSP was released from jail in January after serving one year of his sentence.
Coulson resigned as editor of the News of the World in 2007 after the paper's former royal editor Clive Goodman and private investigator Glenn Mulcaire were jailed for phone hacking.
Only months later, in May that year, he was unveiled as director of communications and planning with the Conservative Party.
He quit his role as Downing Street communications chief in January 2011 after admitting the News of the World phone-hacking row was making his job impossible.
Coulson gave evidence over two days during Sheridan's trial in December 2010.
The trial, which lasted almost 12 weeks, was one of the longest of its kind in Scottish legal history.
Former Scottish Socialist Party (SSP) leader Sheridan represented himself after parting company with QC Maggie Scott.
He was convicted of five out of six allegations in a single charge of perjury relating to his evidence during the civil action at the Court of Session in Edinburgh.
His wife Gail was on trial along with him but was acquitted of lying to the court during his successful defamation action against the News of the World in 2006.
During the three-month High Court trial, Sheridan said he was the victim of a "vendetta" by the police and a "conspiracy" involving the Sunday newspaper and former colleagues within the Scottish Socialist Party.
On his release from jail in January he vowed to continue the fight to clear his name.
Speaking about Coulson's detention, a spokesman for Scottish First Minister Alex Salmond said: "These are matters properly for the Crown Office and the prosecution authorities."
The spokesman recalled that Mr Salmond had spoken about the Strathclyde Police investigation into phone hacking in Holyrood earlier this month.
The First Minister told MSPs then: "At present we have a live police inquiry in Scotland which has up to 40 officers working on it. That is a huge commitment of resource by Strathclyde Police.
"I know that because of the inaction in the past of the Metropolitan Police, people are sceptical about police inquiries into these matters, but there is no reason to be sceptical about the inquiry by Strathclyde Police.
"It is a live inquiry, huge resources are being devoted to it and the expectation is that the force will pursue the evidence without fear or favour and produce effective results."
Mr Salmond also stated: "At all times the rule of law will be upheld in Scotland."