Paddy Power Betfair has been fined £2.2m by the gambling watchdog for failing to protect customers and stop stolen money being gambled.
The betting site failed to adequately interact with customers who were displaying signs of problem gambling and to carry out anti-money laundering checks, an investigation by the Gambling Commission found.
The company will make a £1.7m payment to charity Gamble Aware and will return £500,000 to the impacted parties.
“As a result of Paddy Power Betfair’s failings significant amounts of stolen money flowed through their exchange and this is simply not acceptable. Operators have a duty to all of their customers to seek to prevent the proceeds of crime from being used in gambling," Richard Watson, Gambling Commission executive director said.
“These failings all stem from one simple principle – operators must know their customer. If they know their customer and ask the right questions then they place themselves in a strong position to meet their anti-money laundering and social responsibility obligations.”
In the five cases from 2016 probed by the commission, two customers were using the betting exchange and three were gambling via Paddy Power's website and high street shops.
Paddy Power Betfair chief executive Peter Jackson said: "We have a responsibility to intervene when our customers show signs of problem gambling.
"In these five cases our interventions were not effective and we are very sorry that this occurred.
"In recent years, we have invested in an extensive programme of work to strengthen our resources and systems in responsible gambling and customer protection.
"We are encouraged that the Gambling Commission has recognised significant improvement since the time of these cases in 2016.
"This work is continuous and we are committed to working in partnership with other operators, and with the Commission, to become better and better at protecting customers.”