The five-strong team, led by one of the world's top safe crackers, planted bugging devices to monitor security guards for the 'beautifully executed operation'.
Judge Fabyan Evans told the three who were arrested: 'This must have been one of the most sophisticated burglaries of commercial property that has taken place in recent years.'
Middlesex Guildhall Crown Court, Westminster, was told the gang's target was a safe containing gold, platinum, diamonds and other gemstones.
They thought the haul would be worth pounds 1m. But even if they had got away with it, the value was less than a fifth of that. The plan was foiled when police saw the balaclava-clad men on rooftops.
Two escaped by abseiling 70ft down the back of a five-storey building in New Bond Street. The third was seen climbing through a skylight.
Roy Saunders, 60, the mastermind of the operation, who has opened safes for the police in the past and is regarded as probably the best professional safe-breaker in the world, was caught as he crouched in the basement of a shoe shop next door.
Arrested with him were Robert French, 45, a locksmith, and Robert Reed, 49, a building developer.
They were found guilty at an earlier trial of conspiring last October to burgle New English Artworks, which manufactures watches for Cartier.
Peter Moss, for the prosecution, described the crime as a 'beautifully executed operation along the lines of the Pink Panther or League of Gentlemen films'. It involved detailed planning including one of the gang posing as a window cleaner the day before the raid to check on security.
The video cameras were rendered useless and bugging devices were planted to monitor Group 4 security men guarding the five-storey building. The court heard that thousands of pounds of equipment was found in Reed's car.
Reed, of Islington, north London, and French, of Romford, Essex, claimed they had been planning to raid the shoe shop and offices in the building next to the workshop.
Saunders, of West Crawley, Sussex, insisted he had been too drunk to remember anything of the evening.
Michael Bromley-Martin, for Saunders, told the court that since his client was found guilty he had been hounded in prison by fellow inmates wanting to share his safe-breaking knowledge.
'He has been in Wandsworth prison for two to three weeks and there has been a steady stream of potential criminals coming to his door asking all kinds of questions about safes and locks.
'It is plain that Mr Saunders is determined never to give out this information and not to betray the learning he has come to acquire over the years, as he plainly did on that night in 1992.'
The judge told the three that they had clearly put in 'considerable research' in planning the crime.
He added: 'It is rare nowadays that an offence of this kind that involves such considerable profit, involved no violence. Quite why men of your age became involved in an offence like this, remains a mystery to me.'Reuse content