Sky Bet has been fined £1m for failing to protect vulnerable customers, the Gambling Commission has said.

It did not prevent problem gamblers who had self-excluded from its websites from betting, the watchdog said.

Sky Bet chief executive Richard Flint said the firm accepted that it “needed to do more” to stop self-excluded gamblers from opening duplicate accounts.

He added that Sky Bet had tried to return the money that was gambled.

People who feel they are having trouble controlling their gambling can ask betting firms to refuse their service.

But 736 self-excluded Sky Bet customers were able to open and use duplicate accounts.

In addition, about 50,000 people who had excluded themselves received marketing emails, texts or push notifications through a mobile app, the Gambling Commission said.

And 36,748 customers did not get the balance on their account returned after self-excluding.

Richard Watson, Gambling Commission programme director, said: “This was a serious failure affecting thousands of potentially vulnerable customers and the £1m penalty package should serve as a warning to all gambling businesses.

“Sky Bet reported the issues to us quickly, co-operated with us and has taken this investigation seriously.”