The Gambling Commission cites “systematic failings” at Ladbrokes Coral between 2014 and 2017.
Several on-course bookies failed an underage betting test at this year’s Royal Ascot meeting.
Labour deputy Tom Watson has called for an overhaul of gambling regulation in the UK.
UK regulators say self-excluded gamblers have still been able to bet after changing account details.
Reports claim Ladbrokes paid out £1m to punters who were robbed by a VIP client.
The UK’s gaming regulator is under fire over a perceived failure to protect problem gamblers from FOBTs.