The film, which includes scenes where a teenage girl sews her own mouth shut, will be shown online and in cinemas before films rated 12A and above.

It is part of a £1.2 million campaign launched by children's charity Beatbullying in memory of bullied schoolgirl Megan Gillan.

The 15-year-old, a student at Macclesfield High School in Cheshire, took a fatal overdose of painkillers after being bullied on social networking site Bebo.

Her family endorsed the campaign and said they hoped "no other family suffers the loss we have".

The advert promotes a website, cybermentors.org.uk, which allows young people who have been bullied to help each other and discuss their problems.

A spokeswoman for Clearcast, which decides which adverts can be shown on British television, said it was felt some scenes would be viewed as offensive.

Beatbullying's chief executive, Emma-Jane Cross, said: "We are proud of this advert and the way it makes you stop and understand the impact bullying can have on its victims. But we were disappointed that Clearcast refused to let this advert go on to TV. We know that 69% of young people have been bullied and it is imperative that people know cybermentors.org.uk is there to give them support.

"If just one more vulnerable young person gets the help they need from CyberMentors, then all of the hard work and generous donations put into this advert will be proved worthwhile."

A statement released by Megan's family said: "We believe Megan would have supported and benefited from CyberMentors, so this dedication is a fitting legacy and one which, we hope, means no other families must suffer the loss we have."