Gambling giant Entain, which owns well-known brands such as Ladbrokes, Coral, Gala and Foxy Bingo, has been forced to pay out £17m for "completely unacceptable" safeguarding failures.
The FTSE 100 company, which reported an after-tax profit of £260.7m in 2021, has also been warned by the industry watchdog that it faces being stripped of its operating licence in the event of further serious breaches of the rules.
Entain settled following the largest ever enforcement action by the Gambling Commission uncovered anti-money laundering and social responsibility failures.
The regulator pointed out it was the second time the group had fallen foul of the rules to make gambling safer and crime-free.
Entain Group will pay £14m for failures at its online business LC International Limited, which runs 13 websites including ladbrokes.com, coral.co.uk and foxybingo.com.
It will also pay £3m for failures at its Ladbrokes Betting & Gaming Limited operation which runs 2,746 gambling premises across Britain.
All £17m will be directed to socially responsible purposes as part of the regulatory settlement, according to the watchdog.
Additional licence conditions will also ensure a business board member oversees an improvement plan, and that a third-party audit to review its compliance with licence conditions and codes of practice takes place within 12 months.
Gambling Commission chief executive Andrew Rhodes said: "Our investigation revealed serious failures that have resulted in the largest enforcement outcome to date.
"There were completely unacceptable anti-money laundering and safer gambling failures.
"Operators are reminded they must never place commercial considerations over compliance.
"This is the second time this operator has fallen foul of rules in place to make gambling safer and crime-free.
"They should be aware that we will be monitoring them very carefully and further serious breaches will make the removal of their licence to operate a very real possibility.
"We expect better and consumers deserve better."
Social responsibility failures included being slow or failing to minimise certain customers' risk of harm associated with gambling.
The regulator said the operator carried out just one chat interaction with an online customer who spent extended periods gambling overnight during an 18-month period in which they deposited £230,845.
Anti-money laundering failures included allowing online customers to deposit large amounts without carrying out sufficient source-of-funds checks, with one consumer allowed to deposit £742,000 in 14 months without appropriate scrutiny.
Another, who was known to live in social housing, was allowed to deposit £186,000 in six months without sufficient checks.
The company said in a statement: "Entain has entered into the regulatory settlement with the commission in order to bring the matter to a close and avoid further costly and protracted legal proceedings.
"Entain accepts that certain legacy systems and processes supporting the operations of its British business during 2019 and 2020 were not in line with the evolving regulatory expectations of the commission in respect to aspects of social responsibility and anti-money laundering (AML) safeguards.
"However, the group also notes the commission's statement that it found no evidence whatsoever of criminal spending within Entain's operations.
"The issues raised by the commission relate to the period between December 2019 and October 2020, which pre-dates the many changes in the area of safer gambling and AML that Entain has introduced."
The enforcement case comes amid delays to the release of long-awaited government proposals for the gambling industry, thought to be postponed again until after a new prime minister takes office.
Restrictions on the industry were widely expected to be announced last month as part of the review of the 2005 Gambling Act, amid concerns rule changes are needed to cover the growth of online betting.