Teachers in the UK are being bullied by parents and pupils, a new survey has warned.

Cases of homophobic, racist and sexist attacks on social media are becoming the norm according to teachers unions.

In an annual survey of more than 1300 teachers by NASUWT, more than half said they have received threatening or abusive comments from both pupils and parents.

In some of the worst cases, teachers were threatened with rape and in one school a teacher who told a pupil off for swearing was called a “f***ing little lesbian” and told she would be “knocked out”.

In the last 12 months, online abuse has risen from 48% to 55% and effective responses by local government, schools and the police remain low.

The survey showed that 79% of abuse from pupils came from Facebook, with almost a third reporting having seen video of them posted online.

Chris Keates, general secretary of NASUWT, said there should be a “zero tolerance approach” towards online abuse.

He added, however, that only 28% of teachers said their school had an internet policy that makes specific reference to protecting staff from abuse by social media.

One teacher commented: “Senior leaders in schools need more training in dealing with these issues, particularly where they do not have a comprehensive understanding of the way in which social media operates.”

The annual conference of NASUWT takes place in Birmingham this weekend, with Education Secretary, Nicky Morgan, expected to address the gathering on Saturday.