Teenagers are being unfairly labelled as sex offenders for sending explicit messages to each other, campaigners have said.

They say criminalising 16- to 18-year-olds for sending explicit pictures to one another shows how disconnected the political establishment is from changes to technology and social values.

A teenager younger than 18 who takes a nude picture of him- or herself using a cameraphone is guilty of the serious offence of creating child pornography. This is the case even if they are over 16, the age of sexual consent.

In one case last year, a schoolgirl was investigated after texting a topless picture of herself to her boyfriend, who later reportedly received a caution, having forwarded the image to friends after they split up. Police at the time warned that young people could find themselves on the sex offender register.

Myles Jackman, a lawyer who specialises in obscenity law, said: “It’s just not clear enough for young people to know that, despite being over the age of 16 and therefore the age of consent, they can’t take erotic selfies and send them until they are 18.“This disparity between the age of consent – where a person can perform an act – and the age of representation – where a person can record or view that act – seems counterintuitive and dangerously against sex education.”

Jackman is a legal adviser to Backlash, an anti-censorship civil liberties campaign group that is raising the alarm over the discrepancy in the law. The group is extending its remit to give legal advice to young people threatened with prosecution for making sexual images of themselves and sharing them consensually on digital media.

A spokesman said: “When authorities find these images, teenagers themselves become subject to laws originally aimed at stopping child abuse, even though no abuse has taken place. These prosecutions cause immense mental distress, and disruption to education. A prosecution, regardless of sentencing outcome, severely harms the future life prospects of young people.”

The warning comes amid heightened moral panic around young people’s sexuality that campaigners say is being used to justify increasing internet censorship.

A since-discredited NSPCC survey claimed last month that a tenth of 12- to 13-year-olds had reported the “fear” that they were addicted to pornography.

Despite the subsequent revelation that the survey was produced by a marketing company, its results prompted the culture secretary, Sajid Javid, to declare that the Conservative party would introduce further measures to protect children from harmful material.

Concern over the impact of online porn in 2013 spurred the government to announce a scheme to force internet users to decide whether they wanted their provider to block websites showing adult content.

Most major internet service providers have signed up to the scheme, but a report published last year by Ofcom, the communications watchdog, found that about 60% of customers had chosen to switch them off.

In December, the government introduced widely criticised rules that ban producers of pornography from filming sexual activities such as spanking and bondage.

• This article was amended on 6 May 2015. It originally stated that the schoolgirl who texted a topless photo of herself to her boyfriend received a police caution. She did not, but the boyfriend did after distributing it to friends. This has been corrected.