UPDATED on 11th August: The UK’s biggest ever gem heist took place last week when raiders attacked the Graff Diamonds boutique in London’s New Bond Street.

Thursday’s broad daylight Mayfair robbery has now been proclaimed as the UK’s biggest ever gem heist, and the second biggest heist of any kind in UK criminal history.

Robbers got away with an incredible £40 million, but not without brandishing handguns and firing warning shots in the busy London street, including at drinkers in a nearby pub.

Two men, clearly smartly dressed as shown in the photo below, arrived in a black London taxi, calmly paid their fare, and strolled into the shop. The store’s staff even held the door open for the thieves.

Picture from CCTV at Graff Diamonds, supplied by Metropolitan Police

Once inside they produced handguns and waved them at terrified shop assistants.

The robbers grabbed 43 items of gems and jewellery, including diamond necklaces, rings, earrings, bracelets and watches. The total value of the haul has been put at a phenomenal £40 million by Scotland Yard.

They appeared to know exactly what they were looking for, targeting the most valuable items in specific cabinets.

Having bagged the gems and jewellery the two men grabbed a woman, believed to be a staff member, taking her hostage as they left the exclusive boutique and firing a shot into the floor.

The woman was released in the street but the drama wasn’t over. Drinkers at a nearby pub started to give chase and a second warning shot was fired into the air by the robbers to scare them off.

They jumped into a blue BMW to make their escape but appeared to bungle their getaway by promptly crashing the BMW into a black cab.

The BMW was abandoned in nearby Dover Street, and it was reported that they then continued their getaway in a silver Mercedes, with sightings of a possible accomplice speeding away on a scooter clutching a package. They then appeared to transfer to a third vehicle, a black people-carrier, in Farm Street.

This isn’t the first time that Graff Diamonds in New Bond Street has been targeted. In 2003 thieves made off with a haul of gems and jewellery worth a reported £23 million from the same boutique. It has been reported (including by us) that the 2003 raid on Graff’s boutique was the work of the notorious Pink Panther gang of jewel thieves.

The two men in this robbery apparently spoke with London accents and are not thought to be connected to the Pink Panther gang. Police have speculated that the two men, and the gems, might very well have already left the country.

Graff is one of the world’s most exclusive jewellers, making jewels that have been seen on Kate Moss, Naomi Campbell, Paris Hilton, and the Beckhams.

Some security commentators have expressed surprise that a store which contains over £40m of jewellery operates an ‘open door’ policy, rather than admitting only those who have made an appointment and have had their identity pre-checked.

Following this record-breaking robbery, and a string of others in Graff boutiques around the world, Graff’s insurance company might now insist upon a change of policy.

UPDATE, 20th August: London police have arrested and questioned 2 men in connection with the Graff robbery. This follows the arrest of another man in East London on August 10th and the recovery of a handgun. It has also been established that the two men who went into the Graff boutique had theatrical makeup applied in order to make themselves appear older.