The online operator is to pay £500,000 for failing to follow Gambling Commission rules which protect problem gamblers.

A Commission investigation revealed that Rank failed to interact with a customer who was displaying problematic behaviour, contacted him during a self-exclusion period and did not follow rules for the provision of credit.

The failures relate to a customer who gambled substantial amounts with Rank’s land-based Grosvenor Casino and online at www.grosvenorcasinos.com. In one 24-hour period the customer lost £1m that had been credited to his account.

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.

“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.”