William Hill has been fined £6.2million for "systemic social responsibility and money laundering failures", the Gambling Commission has confirmed.
An investigation into William Hill Group revealed that from November 2014 to August 2016 the bookmaker breached anti-money laundering and social responsibility regulations.
Their inadequate checks resulted in ten customers being permitted to deposit large sums of money linked to crimes, resulting in £1.2million profit for William Hill.
Commission executive director Neil McArthur said: "We will use the full range of our enforcement powers to make gambling fairer and safer.
"This was a systemic failing at William Hill which went on for nearly two years and today's penalty package - which could exceed #6.2 million - reflects the seriousness of the breaches.
"Gambling businesses have a responsibility to ensure that they keep crime out of gambling and tackle problem gambling - and as part of that they must be constantly curious about where the money they are taking is coming from."
One of the issues found was the bookie failing to seek adequate information about the source of a customers funds or ascertaining if they were problem gamblers.
One example saw a punter depositing £654,000 over a nine month period without checks regarding the provenance of the money being carried out.
The body found the customer to be living in rented accommodation and earned £30,000 per year working in an accounts department.
Another saw someone depositing £541,000 in 14 months after a verbal conversation resulted in the assumption the person could earn above £365,000 per year, resulting in no further enquiries.
In later turned out the person in question was earning £30,000 a year and stealing from their employer to fund their gambling habit.
William Hill confirmed in a statement on its website that its online business has "entered into a regulatory settlement with the Gambling Commission" following the identification of a number of cases where "former policies" were insufficient to ensure full regulatory compliance.
William Hill CEO Philip Bowcock said: "William Hill has fully co-operated with the commission throughout this process, introducing new and improved policies and increased levels of resourcing.
"We have also committed to an independent process review and will work to implement any recommendations that emerge from that review.
"We are fully committed to operating a sustainable business that properly identifies risk and better protects customers.
"We will continue to assist the commission and work with other operators to improve practices in the areas identified."