The most popular mobile games in the UK are being advertised without disclosing they contain loot boxes – random in-game purchases which critics say are “exploitative” and “foster addiction”.

The regulator, the Advertising Standards Authority (ASA), says it bans and removes ads which fail to make the clear whether or not a game contains a loot box.

But a BBC investigation found only two of the top 45 highest-grossing games on the Google Play store actually followed those rules.

Dr Jane Rigbye, chief executive of Young Gamers & Gamblers Education Trust (Ygam), called the findings “deeply concerning”.

“In the absence of robust regulation in gaming, it is essential for games to provide clear and transparent information about their features, allowing both parents and gamers to make informed decisions,” she said.

In a statement, the ASA said: “This is an ongoing area of our work, and we’re closely monitoring the sector to discover the scale of compliance and act accordingly.”

However, some say the regulator lacks the teeth to deal with the problem.

“The ASA, although it has upheld some complaints, it takes so long to properly process all of these things – they will go to a company and say, ‘you should comply’, but they don’t comply,” said Leon Y Xiao, a video game regulation researcher at the IT University of Copenhagen.

“People are walking into a video game not knowing the potential risks, and this is assuming that people have even understood the risk of loot boxes to begin with.”

Loot boxes contain random digital items that gamers can only reveal through gameplay or – more controversially – by making a payment.

Game-makers have previously defended them as being akin to a chocolate egg containing a plastic toy, with children not knowing exactly what they are getting until the egg is bought and opened.

But critics say they are in fact a form of gambling, with a report in 2022 by the Norwegian Consumer Council concluding they “often involve exploiting consumers through predatory mechanisms, fostering addiction, targeting vulnerable consumer groups and more.”

The same year, the UK government resisted pressure to regulate loot boxes, saying the video game industry could self-regulate instead.

Trade body Ukie published guidance in July 2023, including the requirement to disclose loot boxes prior to games being purchased, which the industry was given a year to comply with.

But, more than 12 months later, the BBC has discovered the vast majority of major mobile games containing loot boxes are still flouting the rules, with most games only disclosing their presence if would-be players tap a small information button on the Play Store.

Adrian Hon, head of game developer Six to Start, said the games industry had a track record of “conveniently ignoring or forgetting regulations that might interfere with their ability to sell to players”.

“We know that many people, including children, struggle with overspending on loot boxes,” he said, adding they were deliberately designed to be “habit-forming”.

“The least that games companies could do is disclose the presence of loot boxes, but they won’t even do that – it’s an indictment of their priorities and lack of care towards vulnerable players.”

The BBC checked the adverts for the top 45 highest grossing games on Google’s Play Store, which along with Apple’s App Store are where the vast majority of people access mobile games.

Of those 45, 26 were labelled as including loot boxes – 22 of which were being actively advertised at the same time.

However, only two of those titles spelt out the presence of the loot boxes in their ads.

The highest-grossing game on the Play Store to contain loot boxes, Monopoly GO, was among those not to mention random in-game purchases in its adverts.

The game has been downloaded more than 50 million times, generating more than $3bn (£2.37bn) in revenue according to the IP’s owner Hasbro.

Mr Xiao told the BBC the findings were in line with preliminary results of his own research, which has also found around 90% of games containing loot boxes are not disclosing this in their ads.

The BBC has approached Hasbro, Meta and the ASA for comment.

Zoë Osmond, CEO of GambleAware, said she was “extremely concerned” about “gambling-like activities” becoming normalised for children.

“We know from our previous research that many children have reported how their online spaces are ‘saturated’ with content which often blurs the lines between gaming and gambling,” she said.

“Exposure to this gambling-like content from a young age can lead to an increased risk of experiencing gambling harm later in life.”