Heist warning takes the sparkle out of biggest-ever diamond show

Sophie Marceau holds the De Beers Millennium Star that was once again a target for thieves

The world's largest display of diamonds has been shut down after police uncovered a plot to raid the exhibition.

The Natural History Museum in London was so concerned about the potential raiders they have closed the exhibition at the building in South Kensington.

Among the items on display - and almost certainly the target of the suspected thieves - was the De Beers Millennium Star, a 203-carat, pear-shaped diamond, worth about £200m, which was a target for thieves in a foiled robbery attempt on the Millennium Dome in 2000.

The display, which has attracted more than 70,000 visitors since it opened in July and was to run for three more months, was closed immediately.

The intelligence about a robbery was apparently vague, which made it too risky for the police to try to catch the thieves in the act. The enormous number of people - including thousands of children - who visit the museum every day made it too dangerous and impractical for detectives to stake out the building and wait for the gang.

Dr Michael Dixon, the museum's director, said: "Since we began planning this exhibition, we have followed police advice to the letter in terms of ensuring the security of our staff, our visitors, and the exhibition specimens. That advice changed on the afternoon of Tuesday. It indicated a heightened criminal risk to the exhibition.

"The museum's priority is the safety and security of our visitors and staff. Based on police advice, the only responsible course of action in this situation was to close the exhibition."

Other gems included in the exhibition are the Steinmetz Pink, the world's largest pink flawless diamond; the Ocean Dream, the world's largest naturally occurring deep blue-green diamond; and the Incomparable, which at 407.48 carats is the world's third largest cut diamond.

Also on display was Scott Henshall's Spiderman dress, made almost entirely of diamonds, which was worn by the singer Samantha Mumba at the premiere of Spider-Man 2. The tiara worn by Catherine Zeta-Jones on her wedding day was another popular attraction.

The rest of the National History Museum will stay open as usual and all those with pre-booked tickets for the diamond display will receive a full refund.

A spokeswoman for Scotland Yard said: "We have received information that leads us to believe that criminals were planning to target the exhibition. For the safety of staff, visitors and the exhibition specimens, we have advised the management to close the exhibition with immediate effect."

The appearance of the Millennium Star at the museum was the first time it had been seen in public since days before a gang armed with a mechanical digger and nail guns tried to snatch it from the Dome.

The raiders were caught in the act by the police, some of whom were dressed as cleaners. Police had replaced the diamond with a replica. Six men were jailed for up to 18 years each.

It would have been the world's biggest robbery. In a separate case last month, three men were remanded in custody after appearing in court charged in connection with a ram-raid on the high-class jeweller Tiffany & Co. A 4x4 vehicle was driven through the plate glass window at the store in Sloane Square, London, in October.

Police were involved in a high-speed chase with a moped carrying two suspects, that left one suspect dead and the other injured.