A jury has been shown a high-powered nail gun allegedly used by raiders to break through the Millennium Dome's diamond vault.

Brighton man Kevin Meredith, 34, of Auckland Drive, is among those accused of conspiracy to rob a diamond exhibition at the attraction, in Greenwich, London, last year.

The nail gun was bought for £762 cash by one of the gang as they plotted to snatch diamonds worth £200 million from the De Beers Millennium Diamond Exhibition, said Martin Heslop QC, prosecuting.

Terence Millman, who has since died, used a false name and address and also bought a box of three-inch nails, the prosecution alleged at the Old Bailey in London.

Taking the unloaded gun in his hands and pulling the trigger, Mr Heslop told the jury: "You hold it to the surface of the object you want to penetrate.

"It is designed to fire into concrete and steel and can penetrate up to 25 millimetres or one inch of solid steel."

The armoured glass in the vault was three-quarters of an inch thick.

Mr Heslop said the jury would later see that was the gun allegedly used by another of the gang - William Cockran - to fire nails into the vault on November 7 last year.

He was continuing his opening for the prosecution on the third day of the trial of six men accused of plotting to snatch the diamonds - which was foiled by police after a sophisticated surveillance operation.

Meredith denies conspiracy to rob, as do Wayne Taylor, 35, of Tonbridge, Kent; Aldo Ciarrocchi, 31, of Balaclava Road, Bermondsey, and Cockran, 48, of Catford, both south east London; Robert Adams, 57; and Raymond Betson, 39, of no fixed address.

Mr Heslop has alleged the gang's target "was nothing less than the 12 extremely rare and valuable diamonds" on display in the vault at the Dome.

He said the Millennium Star and the Millennium Blue Diamonds "may very well be the rarest and finest diamonds in the world".

He added: "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 case continues.