Websites such as YouTube must be shut down to combat victimisation of staff and pupils by so-called 'cyber-bullies', a teaching union has urged.

The Professional Association of Teachers (PAT) claims such sites give license to bully or humiliate staff and pupils by offering a platform to post malicious mobile phone videos.

The union said abusive text messages or emails are also rife and that tough action needs to be taken.

Delegates at the PAT's annual conference in Harrogate backed a motion demanding that such websites be closed down.

The motion was proposed by Kirsti Paterson, from the PAT's Highland and Western Isles Federation, who said one teacher had been the subject of a death threat posted online.

"Nowhere is safe from cyber-bullying. It can carry on 24/7 through mobile phones and in multiple forms online," she added.

Remarks and images posted online can easily be copied and made available to a global audience.

Catriona Tait, a newly qualified primary teacher from Dundee, said one in four pupils had experienced cyber-bullying at some time.

"Not only are the children and young adults in our care subjected to such torment, it would now appear that members of the profession are becoming victims of cyber-bullying," she said.

"Just a few words entered into the video-sharing site YouTube and a number of short videos featuring members of staff were at my fingertips.

"Nobody should be subjected to such humiliation anywhere, let alone in their place of work," she added.

A YouTube spokesman said the vast majority of people used the site responsibly and "in very positive ways."

"Sadly as with any form of communication, there is a tiny minority of people who try to break the rules. YouTube is part of the Government's Cyberbullying Taskforce, working closely with teachers unions and others," the spokesman added.