One example given by the Gambling Commission was the company failing to challenge a customer who staked £1.3m over a 13-month period, with some of the money stolen from their employer.

This included a technical failure in its systems which allowed more than 7,000 people who had chosen to self-exclude from one gambling platform to still access their accounts via a bingo platform.

The Commission said affected customers, who were able to deposit a total of £3.5m into their accounts and then continue to gamble for more than 13 months, would be getting that money back as part of the penalty.

The bulk of the rest of the sum – £4.25m – would go to fund work aimed at preventing problem gambling, while £62,000 would be repaid to the employer who was the victim of theft.

Sarah Harrison, chief executive at the Gambling Commission, said: “Safeguarding consumers is not optional.

“This penalty package of just under £8m reflects the seriousness of 888’s failings to protect vulnerable customers.

“The 888 sanction package will ensure those affected don’t lose out, that the operator pays the price for its failings via a sum that will go to tackling gambling-related harm, and that independent assurance will be given to see that lessons are learnt.”

The company said it had cooperated with the Commision’s review and agreed a “voluntary regulatory settlement”.

It added: “The company accepts the conclusion of the review and is committed to providing players with a responsible as well as enjoyable gaming experience.”

The penalty comes at a crucial time for bookmakers as they try to fight off a crackdown on in-store fixed-odds betting terminals – dubbed the ‘crack cocaine’ of gambling – amid widespread criticism of stakes of up to £100 per spin.