The majority of teenagers are turning to porn to fill the gaps left by their sex-education lessons, a new survey suggests.

Almost two-thirds of young people have used pornography to find out more about sex, and two-fifths say that it has helped them to understand sex.

The survey of more than 2,500 young people, carried out by the National Union of Students, asked them to rate the quality of the sex and relationship education (SRE) they received in school. More than half said that the issues they needed to know about were not covered in these lessons.

Two-thirds considered their SRE lessons to have been “fair, poor or terrible”, and only a third said that they could practically apply the information covered to their real lives.

For the majority, these lessons simply focused on the biology and mechanics of sex: puberty, contraception, sexual health and anatomy are the subjects most commonly covered in schools.

Fewer than half of survey respondents said that the subject of relationships had been covered during their SRE lessons. And two-thirds said that the issue of consent was never discussed.

Colum McGuire, the vice-president of the NUS, said: “Sex is not a science lesson. People are being left with gaps in their education. SRE is failing millions.”

Jane Lees, the chair of the Sex Education Forum, said: “Consent and relationship safety are real issues affecting students, and sadly they are leaving school with little or no discussion of these topics.”

Fewer than a fifth were taught about lesbian, gay, bisexual or transgender relationships in school. “In a country where we passed an equal-marriage bill, this is the height of hypocrisy,” Mr McGuire said.

Though three-quarters admitted that online pornography created “unrealistic expectations” about sex and sexuality, most said that it was nonetheless a standard part of young people’s lives.

New guidelines for sex-education education, drawn up last year by a number of sexual-health organisations, said that teachers should acknowledge ubiquity of pornography, but should teach pupils to understand the differences between “distorted images of sex” and real-life relationships.

The document, which was the first update to official advice regarding SRT, was backed by the Department for Education.

In response to the NUS survey, a DfE spokesman said that SRE is now compulsory in all secondary schools. “Good-quality relationship education is an important part of preparing young people for life in modern Britain,” he said. “

He added that a new PSHE expert subject group had been set up to support and advise teachers, and to provide new resources where necessary.

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