London: The two men who arrived at Graff Diamonds in Mayfair on August 6 afternoon gave little reason to arouse suspicion.

They had come by taxi, were dressed smartly in suits and, after being shown inside, made no attempt to shield their identities from security cameras. But within seconds, the pair had produced handguns and were threatening staff. Minutes later, they had escaped with the most valuable haul of any jewellery robbery in Britain.

The 43 items, including rings, bracelets, necklaces and watches, had a retail value of £40 million (Dh242 million) and were encrusted with 1,437 diamonds, police disclosed.

Individual pieces included a platinum and gold flower necklace embedded with 268 diamonds.

Britain's previous biggest diamond robbery was thought to have been a £23 million raid, also at Graff's, in 2003.

The two suspects are thought to be Londoners.

Scotland Yard later said one suspect was arrested in connection with the case. The man was not one of the two well-dressed men.

CCTV images show the two walking inside. In making their getaway, the men briefly took a woman employee hostage, releasing her when they climbed into a blue BMW after firing a warning shot above their heads. Their escape was nearly foiled when the car crashed into a black cab.

As the driver and customers from a nearby pub gave chase, one of the men fired another round into the ground.

It is thought that, at some point, the jewels were transferred to a waiting motorcyclist. Police believe that at least two other men acted as getaway drivers.

Detective Chief Inspector Pam Mace, of Scotland Yard's Flying Squad, said: "This was a well-planned robbery with a number of vehicles used to help the robbers escape.