An infamous hardline Scottish nationalist who has lived in exile in Dublin since the 1980s has been convicted of making hoax bomb threats against transatlantic planes flying from Heathrow airport.

Adam Busby, 61, was found guilty of sending the hoax threats warning of alleged bombs on board two aircraft in May 2006 by a jury at Dublin circuit court after a seven-day trial.

Busby, a former soldier originally from Old Kirkpatrick near Clydebank, has described himself as a founder of the self-styled Scottish National Liberation Army and achieved notoriety for his role in orchestrating bomb hoaxes against senior political and legal figures.

He fled Scotland in the early 1980s after facing arrest for terrorism offences and became an influential figure for a small number of young hardline nationalists on the fringes of the Scottish nationalist movement who were attracted by his mixture of republican socialist and revolutionary nationalist rhetoric.

In the latest in a string of convictions, Busby was found guilty today of hoax threats to cause "annoyance, inconvenience or needless anxiety" in emails to BAA by claiming bombs were on board two separate flights due to land in New York. A BAA security manager said that in both cases they were assessed as low risk threats.

Among the SNLA's early targets for its primitive letter bombs, death threats and hoax bomb threats were sent to Margaret Thatcher when she was prime minister, the Prince of Wales and Douglas Hurd, who was home secretary.

The SNLA claimed responsibility for a hoax anthrax attack against Prince William at St Andrew's university and against Jack McConnell when he was Labour first minister of Scotland. It was linked to an attack targeting Cherie Blair at Downing Street in 2001 when aromatherapy oils were spiked with caustic soda.

His son Adam Busby Jr, from Paisley, was convicted in May 2009 of carrying out a campaign involving suspect packages targeting the Scottish National party leader, Alex Salmond, SNP headquarters, Glasgow council and the English-born Scottish Liberal Democrat MSP Mike Rumbes.

Busby Jr was arrested by armed police after sending out six suspect packages containing shotgun cartridges and threats of future bomb attacks; like his father he telephoned journalists to claim the campaign was the work of the SNLA. He had a previous conviction from 2001 when he was jailed for six years for carrying out petrol bombings.

Busby Sr was linked to the cases of several radical nationalists who carried out bomb attacks, letter bomb attacks and hoax bomb attacks in the SNLA's name in the late 1980s and 90s.

In 1993 the former army reservist Andrew McIntosh was jailed for 12 years by the high court in Aberdeen for placing bombs outside oil industry offices and sending letter bombs to the Edinburgh address of the Scottish Office, which was the Whitehall ministry in charge of Scotland.

After his release in 1999 McIntosh was later arrested with two other men on firearms charges on the day of the official opening of the new Scottish parliament building at Holyrood in October 2004. He was found hanged in his jail cell a week later, hours before he was due in court to face the charges.

In 2008 Wayne Cook, an Englishman from Manchester, was convicted of sending miniature vodka bottles spiked with lethal levels of caustic soda to various public figures in the SNLA's name. A Scot, Steven Robinson, pleaded guilty to similar charges at an earlier hearing.

After their convictions, Detective Chief Superintendent Tony Porter, head of Greater Manchester police's counter-terrorism unit, said: "Be in no doubt these men are terrorists. This was not some clumsy joke – it was a serious attempt to cause real harm and intimidation.

"Robinson and Cook's actions would have caused serious injury to anyone who came into contact with the chemical. Had anyone drunk the contents they would in all likelihood have died."