Police are investigating allegations a member of staff at a school had a photograph of herself in her underwear taken from her mobile phone and distributed among pupils.

Gosford Hill School headteacher Dr Stephen Bizley said last night he feared the woman, who appeared to have taken the photo in a mirror, had been the victim of "a vicious and personal act of bullying".

Dr Bizley and the police yesterday confirmed they had launched investigations. He refused to rule out the possibility those responsible for any wrongdoing would be expelled from the school.

He added: "Last week a non-teaching member of staff reported her mobile phone had been tampered with and items stolen from the phone.

"The school launched an immediate and full investigation.

"The education authority was informed and confirmed the school should continue its investigation into what was an unprovoked and personal attack on a member of staff.

"It is understood the staff member concerned also informed the police.

"There is absolutely no suggestion the staff member concerned was at fault and ongoing investigations strongly suggest the staff member concerned was targeted and the subject of a vicious and personal act of bullying.

"At this point I think it's inappropriate to say any more. It's a delicate stage of the investigation. Once the full and true facts are established the appropriate action will be taken by the school."

Thames Valley Police confirmed officers were investigating "allegations of theft".

Incidents of teachers and support staff at schools falling victim to 'cyber-bullying' - involving the use of Internet sites or mobile phones, in particular - are said to be an increasing problem, according to the Association of Teachers and Lecturers.

Christine Gregory, a spokesman for the union, said modern technology left teachers and support staff particularly vulnerable. The union feared that victims might quit the profession as a result.

She said: "It's a national issue. Increasingly it's happening and schools need to have very robust policies to deal with pupils and other colleagues who bully staff.

"Young teachers and support staff are particularly vulnerable because quite often there isn't a huge age difference between the pupils at the school and themselves. It can make life very difficult."

Dr Bizley agreed tackling 'cyber-bullying' was a challenge.

He said: "It highlights again the daily dangers the education profession faces in the world of the Internet and mobile phone technology."

Michael Waine, the county council's cabinet member for schools improvement, added: "Everyone has the right to be free from bullying in the workplace and this is especially true for staff at schools.

"Students need to be held responsible for their actions and their parents must address this behaviour in partnership with schools."