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.”