More than 90% of websites selling ringtones for mobile phones to children and teenagers are misleading them with unclear charges and confusing information, an investigation by the European commission has found.

The tactics include signing up users to subscriptions when they believe they are downloading one-off tunes and using free offers to lure them into long-term paid contracts.

Brussels is to announce this week that it will launch inquiries into dozens of British ringtone websites, in addition to many others across Europe. In a further move against the exploitation of mobile phone users, Viviane Reding, the European Union telecoms commissioner, said that operators had adopted a “bunker mentality” by not reducing their international call charges.

The move on ringtones follows a year-long sweep of more than 500 websites across the 27-nation EU with findings prompting further investigation of 80% of sites for possible breaches of consumer law.

In Britain the proportion was more than 90%, with 39 of the 43 websites warranting further investigation. “Some children as young as five have a phone and young people often see ringtones as a fashion statement,” said Meglena Kuneva, commissioner for consumer protection. “Children are particularly vulnerable consumers and our initial investigation into the mobile services market shows a high number of rogue traders ready to cash in on this.”

The EU investigation pinpointed misleading practices common to the £550m European ring tones market.

Many consumers believe they are buying a single ringtone when often they are agreeing to a £1.50 tune every day or for a weekly subscription. The inquiry also found that the word “free” can be used to offer an unpaid tune while luring consumers into longer-term paid contracts.

The results of the EU investigation will be used by national regulators to force changes in the industry.

PhonepayPlus, the industry body that regulates add-on mobile phone services, has recorded a 108% rise in complaints in the past year, with 4,500 in January to March alone.

Coupled with Reding’s attack on mobile phone international “roaming” charges, it seems the net is closing in on an industry that appears to have little consumer regard.

Operators were asked to reduce their roaming rates – charged when customers travel in Europe – voluntarily and to detail their cuts. T-Mobile, for example, has cut its data roaming charges from £7.50 per megabyte to £1.50. It says the cost of sending texts from EU countries will fall from 40p to 25p from August 30.

Reding will announce her assessment of the operators’ cuts later this week but has already indicated her thoughts.

“Unfortunately the industry has not listened to my call for credible voluntary price reductions,” she said. “This is bad news for all EU citizens who travel abroad, whether for business or for pleasure.”

She added that the EU will now have to work on a “regulatory response to the market failure”.