London - Wielding a mechanical digger and smoke bombs, their getaway boat waiting on the Thames, the villains must have expected little difficulty as they smashed their way into the Millennium Dome, intent on grabbing £350-million (about R3,8-billion) worth of diamonds.
But the gems, including the spectacular 203-carat De Beers Millennium Star, had been replaced with fakes and police were waiting on Tuesday morning as the gang burst into the big tent in east London. Eleven people were arrested without a single shot being fired.
"If this had been carried out in accordance with their wishes, this would have been the largest robbery in the world," said Detective Supterintendent Jon Shatford, who led the operation involving more than 100 officers.
"It was an extremely audacious operation."
Police arrested four people in the vault that usually houses the diamonds and seized another two as they tried to make their getaway by speedboat along the river. Five people were arrested later in south-eastern England.
A spokesperson for the dome operators, the New Millennium Experience Co, said the diamonds are displayed in the dome's money zone and very closely guarded. The Millennium Star is displayed in a reinforced glass cylinder and the area has alarms and security cameras, the company said.
The collection on display at the dome also features 11 large diamonds of a distinctive vivid blue.
Shatford said the robbers, apparently disguised as workmen, drove the digger past security guards about 9.30am (0930 GMT), shortly after the dome opened its doors for the day. As they entered the building, they donned gas masks before unleashing smoke bombs, but none of the dome's estimated 100 visitors were nearby.
Police disguised as cleaners were positioned around the inside of the dome and "as the robbers went into the vaults they effectively imprisoned themselves and were ordered to come out at gunpoint by the officers," Shatford said. The thieves were overpowered as they bashed at the display cases with hammers and sledgehammers, he added.
De Beers spokesperson Kate Evan-Jones said the company replaced the gems with models made of crystal after a tip-off from police.
She described the flawless, pear-shaped Millennium Star is arguably the most perfect large diamond in the world and third largest ever discovered. "It is impossible to put a value on it because of its rarity and uniqueness," Evan-Jones said.
The Guinness Book of Records says the world's largest gem theft was carried out in August 1994 by three men who stole items valued at £30-million from a jewellery shop in the Carlton Hotel in Cannes, France.
The world's biggest bank robbery was executed by guerillas who blasted the vaults of the British Bank of the Middle East at Bab Idriss in Beirut in January 1976, making off with valuables worth £22-million, according to the Guinness Book.
John O'Keefe, executive creative director at the Bartle Bogle Hegarty advertising agency, said the caper could attract more visitors to the struggling and much-derided dome.
"This is the kind of publicity money can't buy," O'Keefe said.
"In my opinion there should an ad in the papers tomorrow with an earth digger parked outside the dome and the phrase 'YOU can get in for just 20 pounds'." - Sapa-AP