The operator's failure relates to a specific customer who, in just 24 hours, lost the £1m credited to his account at Grosvenor Casino.

Richard Watson, Gambling Commission Executive Director, said: “We expect all operators to protect any consumer who maybe experiencing problems with their gambling and operators shouldn’t fall into the trap of thinking that VIP customers don’t experience difficulties."

The Gambling Commission found that Rank Group failed to adhere to rules regarding offers of credit and self-exclusion.

The overseas customer, described by the operator as long-standing and of high net value, had excluded himself from the website for a period of no less than six months in 2016. It was in this time that he was visited at his home by a General Manager of Grosvenor Casinos.

Watson said: “No matter how wealthy customers are, operators still need to monitor them effectively to ensure they aren’t showing signs of problem gambling. It is certainly not appropriate to visit customers during a period when they are self-excluded.

“This penalty package would have been a lot higher were it not for the positive action Rank took in terms of self-reporting their failures and being open and transparent during our investigation.”

Rank Group has accepted the conclusion that there were weaknesses in its system relating to how it managed this customer.

The Gambling Commission views this case as a chance for other operators, both online and land-based, to check their own systems and ensure procedures are in place to notice and prevent problem gambling.