European mobile phone operators have agreed to join forces to obstruct access to child sexual abuse websites.

Leading operators, including Vodafone, Orange and 3, will announce plans today to install technology in their networks that will bar access to thousands of blacklisted sites.

Efforts to ban access to these sites has focused on service providers such as BT, which offer internet services via personal computers, but with internet access increasingly becoming a standard feature on mobile phones, the phone operators are facing increased pressure to take action on their networks.

Under the scheme, which is being spearheaded by the GSM Association (GSMA), the mobile industry's global trade body, customers who, inadvertently or otherwise, try to access illegal sites will be directed to a police warning notice or be presented with a message saying that the site is not available.

The participating companies will also provide hotlines for customers to report any child sexual abuse content discovered via their mobile phones.

The plans will be announced at the Mobile World Congress in Barcelona, the mobile phone industry's annual get-together.

More than 50,000 delegates are expected this year.

Separately, Viviane Reding, the EU Commissioner for Information, Society and Media, will threaten mobile companies today with tough new rules if they do not end alleged “rip-off” rates for consumers accessing the internet on their mobile phones abroad.

She will tell the mobile operators that they must bring down prices by this summer or face new legislation.

The new efforts to obstruct access to sexual abuse sites emerge as Britain's mobile operators face increasing criticism about their failure to safeguard children from unsuitable content on their handsets.

In 2004 a scheme was introduced amid much hype to prevent children accessing pornography, gambling and other adult services on the latest mobile phones.

It included the introduction of a cinema-style “18” classification of mobile content and a service to help parents buying 3G phones for their children to block access to certain sites.

The scheme, which is voluntary, is being reviewed by the telecoms regulator amid concerns that the mobile companies have been slow to carry out their promises.

A spokesman for the GSMA said that making subjective judgments about material available over the mobile internet was not its responsibility.

“We are not policing the net," he said. "That is a different issue. This is about illegal content.”

Last year a report from the Internet Watch Foundation (IWF), which shuts down illegal sites, claimed that as many as one in twenty people had stumbled accidentally at some time across images on the internet of children being sexually abused.

Although Britain has been successful in shutting down illegal child sexual abuse sites hosted here, sites based overseas are accessible from this country.

The IWF provides a list of up to 1,500 sites around the world featuring illegal child sexual abuse. Its members are encouraged to block access to these sites voluntarily.

However, if such sites are located and closed down, the criminals involved in the industry will often open new ones elsewhere on the web.

The wide footprint of the mobile phone providers involved in the GSMA project means that 50 countries will be covered.