Half of teachers say they have noticed an increase in pupils having sexually explicit conversations in the past five years, a survey on the impact of pornography has found.

Nearly 40 per cent of staff in schools and colleges said that the young people they work with had viewed pornography and nearly the same amount said they were aware of pupils “sexting”.

More than three-quarters of staff survey by teaching union the Association of Teachers and Lecturers (ATL) said that they thought pornography should be discussed as part of PSHE or similar lessons, and over half  who did not already teach it said they would be prepared to.

However, the majority said they would have concerns about their school teaching issues surrounding porn, with most worried about the reaction of parents.

A primary teacher told the union: “I work in an inner-city school and am shocked at the way the children use sexual language, and they are under 10. I think more needs to be done in the media to tackle this.”

Education staff said that viewing pornography not only led to greater use of sexually explicit language, but pupils were also more likely to talk about pornography and sexual touching or groping.

A secondary teacher said: “Pornography can be harmful to the social well-being of a child, particularly at an early age, as it gives a warped sense of what ‘normal’ relationships are.

“I have seen Year 7 students omitted from friendship groups because of what they deem as normal after viewing extreme pornography.”

Andrew Simpson, a secondary teacher in Kent, said: “I believe this is the biggest threat to young people today and, unfortunately, we have not kept up with technology and have let young people down. The government must tackle this issue if they don’t want to see the concerning behaviours continue into adulthood.”

Staff taking part in the survey also raised concerns about the amount of training available for teaching about explicit material.

Mary Bousted, general secretary of the ATL, which surveyed 451 school staff, said: “Although pornography is a sensitive issue, the majority of our members feel it’s important young people are taught about the dangers… so they can protect themselves in today’s increasingly sexualised society.

“To do this education staff need high-quality CPD, which is why we repeatedly call for all schools to provide access to good quality sex and relationships education, taught by professionals.”

The survey comes after the House of Lords voted against the addition of an amendment to the Children and Families Bill, which would have made sex and relationships education (SRE) compulsory in all state-funded schools.

Emma Renold, professor of childhood studies at Cardiff University, called for direct action by those most affected by the decision, saying that ten thousand school children should march on Westminster in protest.