A team of hackers based in Russia has published details of a number of high-rolling clients of the UK-based jewellery company, with a threat of much more damage to come if a ransom isn’t paid.

The virtual heist may prove more successful than previous attempts to steal diamonds from Graff. And it could cost the company substantial sums if the UK regulator decides that it was careless in its security policies.

The hackers have already loaded 69,000 confidential documents onto the dark web, according to the UK press. The 11,000 Graff clients targeted so far include Sir Philip Green, according to the UK newspaper Mail on Sunday.

A former colonel in British military intelligence told the newspaper that the leak is a huge problem.

“Given the profile of the customer database, this is absolutely massive,” Philip Ingram said. “This is going to bring the highest levels of international law enforcement down on the gang, and that’s going to give them a whole lot of headaches in trying to get the ransom paid and then get away with it.”

Six hundred UK customers of Graff have had their details stolen, including Formula One heiress Tamara Ecclestone. Saudi Crown Prince Mohammed bin Salman is listed as a Graff client in Monaco, as is Sheikh Mohammed bin Rashid Al Maktoum, the ruler of Dubai, the Sunday newspaper said.

Graff has two outlets in Monaco, one in the Hotel de Paris and the other in the Casino.

Laurence Graff, now 83, left school at 15 and earned money scrubbing floors and cleaning toilets to pay for a part-time education while working as an apprentice in London’s Hatton Garden, the centre of the UK diamond trade. He is now worth an estimated £2.9 billion.

The Information Commissioner’s Office can fine a company that has been careless with client data up to four percent of annual turnover, which in the case of Graff is around £450 million.

Graff responded to the attack by saying: “We have informed those individuals whose personal data was affected and have advised them on the appropriate steps to take.”

PHOTO: Graff’s outlet in the Hotel de Paris