Rohan Thomas, 37, was sentenced at Leeds Crown Court for his involvement in the "terrifying" attack at a warehouse party. A fellow gang member, Steven Crossdale, 27, of Herne Hill, south-east London, was jailed for eight years.
Metropolitan Police informer Eaton Green, 28, received a six-year sentence after the court was told how the three men robbed guests at the party in Nottingham in May 1993.
Cash, jewellery and mobile phones were stolen from 100 people, who were lined up and threatened with guns. Green shot one of them in the foot to allay suspicions that he was an informer.
The court was told that Thomas had entered Britain in March 1993 under a false name and with a false passport. He had several convictions for violence in Jamaica and had been released from jail in 1992 after serving 12 years for shooting at a policeman.
Mr Justice Smedley told them: "The events of that night were extremely serious. It was a terrifying event and people were frightened for their lives."