Antoin Duffy, 39, Martin Hughes, 36, and Paul Sands, 32, planned to kill Adair – who Duffy believed had ordered the murder of dozens of Catholics during the Troubles in Northern Ireland – and his right-hand man Sam McCrory, 51.
At the High Court in Glasgow yesterday after deliberating for three days the jury of five men and nine women convicted Duffy, Hughes and Sands of conspiring to murder the pair.
Duffy and Hughes were also convicted of terrorism charges while two other men, Craig Convery and Gordon Brown, were found guilty of organised crime charges.
They were arrested in 2013 after two major Police Scotland investigations into terrorism and organised crime.
Duffy, from Donegal, was the ringleader of an unaffiliated active service unit inspired by dissident republicanism and planned to carry out the double murder with Sands and Hughes while on home leave from prison, police said.
Operation Hairsplitter was set up in September 2012 to investigate an attempt to procure firearms, including an AK-47, by the gang led by Duffy.
It was feared that if the murders had been carried out it would have had huge ramifications on both sides of the Irish Sea. As a result MI5 authorised the bugging of Duffy’s flat.
Duffy, Sands and Hughes were arrested in October 2013 and charged under the Terrorism Act and also with conspiracy to murder.
In January 2014 Convery and Brown were arrested and charged with directing serious organised crime.
Adair, 51, was a leading figure in the UDA during the Troubles in Northern Ireland and moved to Scotland after being released from prison as part of the Good Friday Agreement.Judge Lady Scott deferred sentence on all five men until next month and ordered background reports on all of them and a psychiatric report on Duffy.
She told the jury they would be excused jury service for life and added: “The court is enormously grateful to you. You have dealt with a particularly difficult case involving really serious charges.
The five convicted men showed no emotion as they were led to the cells.
Detective Superintendent Andy Gunn, who led Operation Hairsplitter, said: “Duffy was the main instigator of the plot to kill two men, due to his twisted ideology to further the aims of dissident republican terrorism.
“This was not sanctioned by anyone of a higher authority within those circles, but was driven by Duffy’s own sympathies.
“He is a dangerous man who was determined to see this conspiracy through to its conclusion.
“I have no doubt that were it not for the intervention of the authorities in an operation led by Police Scotland, we would have been left investigating a double murder in an act of terrorism carried out in our communities.
“Duffy had significant influence to persuade his associates to join the conspiracy, prepare for the act of murder and acquire the weapons to carry it out.
“The streets of Scotland are safer now that he, Sands, Hughes, Brown and Convery have been convicted today.
“It brings two complex and challenging Police Scotland investigations to a successful conclusion.”
Lady Scott ordered the interpreters’ booths at the back of the high-security court to be locked during the trial after fears from defence counsel that their confidential conversations could be overheard by police.
She took this decision after it emerged plainclothes officers were spotted in the three booths at the back of court three by defence counsel in the fourth week of the trial and one was listening in on headphones.
The High Court in Glasgow heard that three officers, one of whom had given evidence and one who was on the witness list – were watching and listening to proceedings – but no-one told the judge, the prosecution team or the defence lawyers.
When this was discovered, lawyers feared their private discussions and with the accused could have been eavesdropped.
The discovery was made by accused Duffy’s QC Derek Ogg on the 21th day of the trial.
Advocate depute Paul Kearney, prosecuting, told the court the plainclothes officers had been sitting in the booth and taking notes during the trial to highlight any potential witness security measures.
A major drug smuggling trial collapsed in 2004 after officers were spotted in the booths listening in to the trial.
The booth incident was not the only concern that halted the trial’s smooth progress. A female juror was removed after it was discovered that her husband was a member of the Orange Order.