Playing for high stakes: the four men 'who tried to pull off the world's biggest robbery' on a bulldozer

Clad in gas masks and body armour, a four-man gang smashed their way into the Millennium Dome in a mechanical digger, intent on what would have been the biggest robbery the world had seen, the Old Bailey was told yesterday.

Their target was the display of 12 De Beers diamonds, worth at least £200m and described as "perhaps the rarest and finest" gems on the planet. The attempted robbery in November last year was the result of months of careful planning by a team of professional criminals, the jury was told.

The expected getaway was to be equally audacious, with a high-powered speed boat and its driver waiting on the banks of the river Thames ready to whisk the robbers and their multimillion-pound haul across the water to a van and another waiting driver.

But the heist – which would have been the "robbery of the millennium" it was claimed – was foiled by a team of dedicated detectives who, posing as Dome workers and tourists, caught the gang red-handed.

The incredible story of the Dome diamond heist was recounted at court 2 of the central criminal court in London yesterday at the opening day of the trial of six of the alleged gang members accused of plotting the robbery.

Aldo Ciarrocchi, 32, from Bermondsey, William Cockran, 49, from Catford, both south-east London; Robert Adams, 58, from north London; Raymond Betson, 40, from Chatham, Kent; Kevin Meredith, 35, from Brighton, East Sussex; and Wayne Taylor, 35, from Tonbridge, Kent, all deny conspiracy to rob the De Beers Millennium Diamond Exhibition – with others – between 7 July and 8 November 2000.

Outlining the prosecution's case, Martin Hislop QC, said the gang's target "was nothing less than the 12 extremely rare and valuable diamonds" on display at the famous attraction. He said the 777-carat Millennium Star and the 11 Millennium Blue Diamonds "may very well be the rarest and finest diamonds in the world".

The gems were on display in two armour-plated cabinets, each costing £50,000, that were protected by elaborate security including alarms, 24 surveillance cameras, and 2 cms of reinforced glass.

Mr Hislop told the jury: "They were playing for very high stakes. This was no ordinary robbery. The value of the diamonds is conservatively estimated, and I will pause here, at £200m.

"Had they succeeded, it would have ranked as the biggest robbery in the world in terms of value. It could properly be described as the robbery of the millennium."

"The operation was planned professionally, down to the last detail," added the barrister.

It was about 9.30am on Tuesday 7 November, shortly after the Dome had opened for the day's visitors, when, it was alleged, Messrs Cockran, Ciarrocchi, Betson, and Adams, climbed aboard a specially customised JCB earth mover.

Mr Hislop said: "It is a very large and powerful bulldozer-type vehicle. An enormous galvanised steel shovel at the front. When driven fast and with criminal intent, it's extremely frightening."

The digger smashed through the perimeter fence and the side of the Dome and was driven up to the vault holding the diamonds – at the centre of a covered exhibition.

"No doubt an armoured tank would have suited their purpose," Mr Hislop said.

But unlike a military vehicle, a JCB could approach the Dome without suspicion.

"They could use this force and power to smash their way into the Dome and approach its exhibition vault – allowing them some protection inside."

Mr Hislop continued: "It would cause terror to those outside as it approached. Then, it could transport them at speed by the quickest route."

The gang was fitted with gas masks and body armour and armed with smoke grenades, two-and-a-half pints of ammonia to spray into people's faces, sledgehammers, wire cutters, a nail gun, and top specification radio and scanning equipment to eavesdrop on the police, the jury heard.

Once they had smashed their way into the diamond cabinet and snatched the gems. the gang planned to drive the digger to the nearby Queen Elizabeth pier where Mr Meredith, a charter skipper, was waiting in a speed boat capable of 55mph, it was alleged. Like the men on the JCB, he was arrested at the scene.

On the opposite side of the river was a man called Terry Millman, 56, who was waiting in another getaway van at the other side. The robbers had even obtained roadworks signs around the getaway van to allay suspicion as it waited for the arrival of the boat. Mr Millman was arrested but died from natural causes before the trial. The police suspect that there may have been a third getaway vehicle to switch from the van, but nothing was found.

Mr Taylor, a horse dealer, was not at the crime scene on the day of the heist but he helped in the planning of the operation, the court heard. The meticulous care in which the gang prepared for the job included two practice, or "dry", runs and extensive surveillance work, it was claimed.

But, all the time, unbeknown to the alleged gang members, the police were watching and waiting for them to strike.

"It was a remarkable police operation. But for their intervention they [the gang] would have got away with £200m worth of diamonds," said Mr Hislop.

Acting on intelligence that someone may be planning to steal the diamonds, the Metropolitan Police set up an intensive surveillance operation, including secretly watching two farms in Kent and a disused coalyard in south-east London.

Detectives watched as a number of stolen cars, the JCB, and two speedboats were hidden at the three sites, it was claimed.

Extra security measures were put in place at the Dome, including the deployment of undercover officers inside the exhibition centre and extra monitoring of the fixed surveillance cameras.

The jury will later be shown footage of the digger crashing into the Dome and the undercover officers leaping to action.

"Cockran, Betson, Ciarrocchi and Adams were all caught red-handed at the scene with the JCB in the Dome having launched their attack and smashed their way in. Meredith was the speedboat driver caught on the boat waiting," said Mr Hislop. The trial continues.