The gambling industry is turning a "blind eye to dirty money", the deputy Labour leader has said, after William Hill was fined £6.2 million for systemic failures.
A Gambling Commission investigation revealed that between November 2014 and August 2016 the bookmaker breached anti-money laundering and social responsibility regulations.
It also found that senior management failed to mitigate risks and to have sufficient staff to ensure that processes for adhering to the regulations were effective.
The commission said William Hill allowed 10 customers to deposit large sums of money linked to criminal offences, that saw gains of more than £1.2 million for the company.
Deputy Labour leader Tom Watson tweeted: "William Hill has just been fined £6.2 million by the Gambling Commission for accepting money from criminals without carrying out proper background checks.
"And this is an industry that talks about 'responsible gambling'. They're turning a blind eye to dirty money."
The regulator said some of the issues it found included the bookmaker not adequately seeking information about the source of punters' funds or establishing whether they were problem gamblers.
Examples of failures included one customer being allowed to deposit £541,000 over 14 months, after an assumption based on a verbal conversation was made that their potential income could top £365,000 a year.
With no further probing undertaken, the commission said that in reality this person was earning £30,000 a year and was stealing from their employer to fund their gambling habit.
Another example saw one punter allowed to deposit £653,000 in 18 months - triggering a financial alert that resulted in an "amber risk" grading which should have been reviewed by managers.
But this did not happen and the individual was able to continue gambling for another six months despite continuing to activate financial alerts, the commission said.
Executive director of the Gambling Commission Neil McArthur said they will use the "full range" of enforcement powers to ensure gambling is 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," he said.
"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."
As a result of the investigation, William Hill will have to pay more than £5 million for breaching regulations and divest itself of the £1.2 million it earned from transactions with the 10 customers.
The Gambling Commission also said that, where victims of the 10 customers who used cash linked to crime are identified, they will be reimbursed.
If further incidents of failures relating to the case emerge, William Hill must also strip itself of any money made from these transactions, the commission said.
According to the regulator, the bookmaker will also have to appoint external auditors to review the effectiveness and implementation of its anti-money laundering and social policies and procedures, and share findings with the wider industry.
William Hill chief executive William Bowcock said the company fully co-operated with the commission and has introduced "new and improved policies and increased levels of resourcing".
"We are fully committed to operating a sustainable business that properly identifies risk and better protects customers," he added.
"We will continue to assist the commission and work with other operators to improve practices in the areas identified."