Tens of thousands of schoolchildren have been caught sending explicit text or picture messages by their teachers in the last three years, according to a new investigation. More than a third of cases involved children aged 12 or 13, according to figures obtained by the Times, while more than 10% of cases involved "a non-school adult".

Politicians and charities are now calling for schools to teach children how to protect themselves from grooming by pedophiles – and from getting into legal difficulties themselves.

Maria Miller, the Conservative MP for Basingstoke, who chairs the Women and Equalities select committee, said that mandatory sex education is needed to help address the "appalling" effect that sexting has on youngsters. She called on education secretary Nicky Morgan to oblige schools to report sexting by pupils under the age of 18 to police.

Should schools police sexting?

"I have changed my position on it. I used to think it should be schools who decide what's appropriate, but the way the internet is impacting on young people's lives – and particularly young girls – leaves them in need of far greater support," she told the Telegraph.

"My concern is that you could have grooming," she said." The revised guidance was that schools should be looking to report cases to police, but I think that is not strong enough and it leaves it open to interpretation by head teachers."

The Times' investigation of 50 of Britain's secondary schools found 1,218 pupils had been caught sending or receiving salacious messages since 2012. It concluded that 44,112 pupils could be involved if numbers were scaled up nationally – and that true figures could be much higher still, if as suspected most cases are not caught by schools.

The Times reported several particularly worrying examples, including a 16-year-old girl who sent explicit images to a convicted paedophile; a 13-year-old girl from the same school who sent explicit videos to an unknown man on Facebook; and a 12-year-old girl who sent topless images of herself to an "array of male students" from the same school in West Sussex. At another school in Yorkshire, nine non-school adults have been implicated in sexting with minors since 2014.

No compulsory sex ed in schools

An NSPCC spokesman told the Times that the numbers were "extremely worrying".

"Sexting can make young people targets for sex offenders or set them up for bullying by their peers," he said. "These figures reflect our experience that sexting among children is now seen by them as part of everyday life."

Morgan told the Times that making sex and relationship education compulsory for schools was "under review", but that the government had no current plans for this to be added to the National Curriculum or for academies and free schools to be required to teach it.

"Schools have a responsibility to make sure children know how to stay safe online and when using technology and social media," she said. "Good schools are already doing this well, and building on their work we're asking all schools to put in place stronger measures protecting children from harm online."

The perils of sexting

  • While, in most cases, it is legal from anyone over the age of 16 to have sex in the UK, taking and distributing 'indecent' images over email or by a phone message of anyone under the age of 18 is illegal – even if all the parties involved consent to the image being taken, sent and received.
  • What precisely constitutes an 'indecent' image is not defined in law, but pictures or videos of breasts, genitalia and sex acts are usually considered 'indecent'.
  • Sending someone an unwanted sext – such as a notrious 'dick pic' – can also be a criminal offence. And forwarding on a sext, or a screengrab of one, to another person, is an offence under civil law.
  • The Child Exploitation and Online Protection Centre (CEOP) made a 10-minute drama showing the unintended consequences of sexting, aimed at teenagers.