The hitherto lawless world of online entertainment has began to adopt the same ratings system that governs British cinemas. The British Board of Film Classification said yesterday that its online ratings scheme, BBFC Online, which features the familiar U, PG, 12A, 15 and 18 certificates, would give parents unprecedented information about what their children were watching via the internet. Online stores and services that sign up to the voluntary scheme will be required to rate downloaded and streamed films, video games and television programmes.

David Cooke, the board’s director, said that members would also be required to block children from accessing inappropriate content.

He gave a warning to parents and providers that the vacuum in online classification would probably be filled by US censors, who were taking a more relaxed attitude to scenes of violence and horror in entertainment.

In 2007, several blockbusters rated 15 in Britain were awarded a PG13 certificate by the Motion Picture Association of America, allowing children aged 13 and over in the US to watch them unaccompanied by parents. The films included Cloverfield, Disturbia and I Am Legend.

“Different, but equally significant, points of divergence can be identified between the standards applied by the various European classification bodies,” Mr Cooke said. “For example, French and British attitudes to children being exposed to graphic sexual representations are poles apart.” He said that the discrepancies underlined the need for a British ratings system to cover online entertainment.

A report commissioned by the BBFC, and carried out by the market research company TNS, suggests that 63 per cent of adults (74 per cent of parents) are worried about downloadable videos that do not come with independent advice and labelling, while 84 per cent (91 per cent of parents) want to see BBFC ratings extended to all online content.

Until the launch of BBFC Online, there was little independent classification of online entertainment. Mr Cooke said: “We are world leaders in this, for sure. There is nobody else doing this. No other media regulator is this far down the road to providing a scheme that allows people to make informed choices about downloadable content in the knowledge that the members providing the films and games are being properly monitored.”

Developed over 18 months, the BBFC Online is a response to demands for consistency from both the public and the film industry.

Three Hollywood studios, Walt Disney Studios, Warner Bros and 20th Century Fox, have already joined t h e scheme, and the BBFC expects that most distributors and vendors will follow suit.

Mr Cooke said he expected that a tiny minority of producers, who create films featuring extreme, often sexual violence, would eschew the scheme.

Classified films, programmes and games will carry a white version of the BBFC’s instantly recognisable “black card”, containing the appropriate category symbol and consumer advice specific to them.

The precise “gatekeeping” mechanism used to stop underage viewers from watching unsuitable content will be left to individual organisations. Existing examples include services such as NetIDMe, where parents can register their child’s details with an independent third party, and PIN-controlled accounts for children.

Margaret Hodge, the Culture Minister, said that the scheme would help parents “gain greater confidence that their purchases are appropriate before they commit themselves”.

Peter Johnson, head of policy at the BBFC, said: “If we don’t get people to sign up to the BBFC system, then it will default to the MPAA ratings, which don’t keep kids out of violent films and which don’t reflect UK public opinion.”

How Britain rates

The Simpsons Rated PG in Britain. but a PG13 in the US because of “irreverent humour throughout”

This is England Rated 18 in Britain because of racist violence and language. Rated suitable for all in France, with a warning Inside

Deep Throat 18 in Britain for sexual content. Rated suitable for children aged 12 and over in France

Brokeback Mountain 15 in Britain. Rated suitable for all in France, but only for those aged 17 and over in the US

Cloverfield 15 in Britain because of threats and horror, but PG13 in the US

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