Its four members - Martin O'Connell, Eddie Butler, Harry Duggan and Hugh Doherty - terrorised London in the mid-1970s.

They were responsible for the Guildford and Woolwich pub bombings which left seven people dead, as well as the murder of broadcaster and author Ross McWhirter.

They got their name after taking a couple hostage in Balcombe Street following a London street battle, and surrendering after a six-day siege.

The siege was sparked by a shooting incident at a Mayfair restaurant, leading to a police chase.

The gang's six-day stand-off, when they held a middle-aged postal worker and his wife hostage in a house in Marylebone, ended in surrender when they heard on the radio that the SAS was to be sent in.

Bomb attacks

The Balcombe Street siege started nine days after the gang shot Ross McWhirter outside his home in Enfield, north London.

Mr McWhirter, co-author of the Guinness Book of Records with his brother Norris, was killed because he had offered a £50,000 reward for the arrest of the terrorists after they carried out a string of attacks.

These included bomb attacks on military and "establishment" targets and shootings at clubs, hotels and restaurants.

Their booby-trap devices killed Captain Roger Goad, an explosives expert, and cancer expert Professor Gordon Hamilton-Fairley, who was mistakenly killed by a car bomb.

Gang members had also thrown other explosive devices - some packed with bolts or ball bearings to cause maximum damage - through the windows of crowded restaurants in London.

Life sentences

At their Old Bailey trial, the gang members faced 25 charges, including seven murders.

They were also accused of conspiring to cause explosions throughout 1975, and falsely imprisoning the couple during the siege.

They were found guilty, and in February 1977, O'Connell, now 47, Butler, 49, and Duggan, 46, were sentenced to 12 life sentences.

Doherty, 48, a brother of Pat Doherty, a leading and influential figure within Sinn Fein, received 11 life sentences.

The trial judge, Mr Justice Cantley, recommended that the men should serve not less than 30 years.

After serving 23 years in UK jails, the four men were transferred to the high-security wing of Portlaoise Prison, 50 miles west of Dublin, early last year.