Makers of mobile games that pressure children to purchase in-app items, or which allow them to do so without responsible adult supervision, could soon be brought to task by the UK Office of Fair Trading (OFT).

The OFT has published a set of principles for the mobile app industry to adhere to when developing apps for children, and opened them to consultation. This follows an OFT investigation launched in April, looking at whether freemium apps are pressuring or encouraging children to pay for additional content.

Many free apps offer users the ability to pay for various services and content such as upgraded membership, virtual currencies — in the form of coins, gems or fruit — and new levels or features.

Concerns prompted by the investigation include the use of unfair or aggressive commercial practices to encourage children to purchase in-game items. For example, a game could imply that a player was letting down other players and characters if they fail to make a particular in-game purchase.

In response, the principles state that in-game payments can only be taken if the payment account holder has given informed consent. This should stop children racking up large bills for in-app purchases they have made without parental knowledge.

In March, Apple settled a lawsuit filed by a group of parents claiming that the App Store purchasing policies allowed children to spend large amounts of money too easily when unsupervised. The company subsequently flagged freemium apps with in-app purchasing functionality to alert parents.

Just this week, Apple added a Kids category to its App Store, providing a clear distinction of which age groups apps are aimed at, and listed titles should adhere to rules for apps aimed at younger consumers.

“These principles provide a clear benchmark for how games makers should be operating. Once they are finalised, we will expect the industry to follow them, or risk enforcement action,” said Cavendish Elithorn, executive director of the OFT.

The OFT investigation also found a general lack of transparency about costs and other information that could influence an individual’s decision to play or download a game. Meanwhile, the distinction between spending in-game currency and real money is blurred in some cases, a practice likely to breach consumer protection law.

Other principles proposed by the OFT include consumers being told up front about any potential in-game costs or advertising, and if personal information will be shared with third parties.

The investigation covered 38 games and the OFT is sharing its principles with similar organisations around the world. The watchdog is inviting responses to the consultation until 21 November.