New restrictions designed to make online casino games less intensive and safer have been announced by the Gambling Commission.
They include the introduction of limits on spin speeds, as well as a permanent ban on features that speed up play or celebrate losses as wins.
Operators must clearly display to the player their total losses or wins.
The Gambling Commission said online operators would need to implement the new rules by 31 October.
The moves come in response to concern over what are known as online slot games - that is, games designed to mimic slot machines in real-life betting shops and casinos.
These account for an estimated 70% of online casino games.
According to the Gambling Commission, these slot games have by far the highest average losses per player of online gambling products.
Online slots and similar casino-style games have come to dominate Britons' spending on gambling. The British public spent £2.2bn on online slot games in 2019, according to the Gambling Commission, and some estimates say the UK now accounts for 15% of these types of games.
The Commission has already cracked down on one of the bookmakers' cash cows, the fixed-odds betting terminal. on which customers can play casino games in shops. Now they have gone after the online equivalent. The new measures are aimed at reining in the power and addictive nature of the games and giving the customer more of a chance to rein in spending.
Gambling regulation in the UK appears headed for a shake-up. The commission has been criticised by some MPs for being toothless and ill-equipped to cope with the shift online. At the end of last month, the government quietly announced a consultation on how the regulator should be funded, with an acknowledgment that it was a small organisation, given the size of the industry it had to police.
A big test may come later this year, with indications that there may be a ban on gambling companies sponsoring the shirts of football and darts players. That would be unpopular not just with the companies, but also the sports authorities and clubs, who have become reliant on the sponsorship income.
Another change being introduced is a ban on reverse withdrawals - a function which allows consumers to re-gamble money they had previously requested to withdraw.
"Evidence shows that reverse withdrawal functions present a risk to players because of the temptation to continue gambling," said the Commission.
"In addition, the slot features being removed or more closely controlled have been associated with increased intensity of play, loss of player control or binge play."
Sports, Tourism and Heritage Minister Nigel Huddleston welcomed the measures, saying they would "help curb the intensity of online gambling, introducing greater protections that will reduce the risk of gambling-related harm".