File photo: The material used in the study included films, TV or pictures depicting actual or simulated pornographic scenes or nudity.

London - Middle-class children typically view porn by the age of 12 and engage in their first sexual activity the following year, according to a study.

It found that the younger they began viewing sexually explicit images, the earlier they went on to engage in sexual activity.

Young women who regularly watched more porn than average were more likely to have higher numbers of sexual partners.

The research was carried out mainly on middle-class students from the University of Buckingham. A total of 42 women and 31 men aged 18 to 25 answered a questionnaire on their porn-viewing habits and sexual behaviour in the previous six months.

The study found that on average, those who had started viewing sexual imagery from the age of 12 onwards had their first sexual encounters the following year.

Sexually risky behaviour – including having multiple sexual partners and sex at a young age – is thought to be fuelling a rise in sexually transmitted diseases among teenagers and young adults aged 15 to 24.

The material used in the study included films, TV or pictures depicting actual or simulated pornographic scenes or nudity, as well as explicit adverts and music videos. Sexual activity was defined as including kissing and foreplay but stopping short of intercourse.

The youngest a respondent reported first looking at pornography was six.

The researchers said the age at which participants were first exposed to sexually explicit material predicted how likely they were to engage in sexual behaviour at a younger age for both men and women.

While women who actively sought out pornography had higher numbers of sexual partners, those who viewed sex scenes incidentally – such as in a TV show, film or music video – were not found to be more prone to risky sexual behaviour such as engaging in one-night stands or not using contraception.

Full intercourse happened on average by the age of 16 in the sample, although one respondent reported first having sex at 13.

As adults, the respondents had on average 12 sexual partners, with the highest number reported being 60. One respondent admitted having 48 one-night stands.

Watching porn frequently was not found to lead to a higher number of sexual partners for adult men.

The authors said that the age at exposure was a more significant factor than the quantity viewed in adulthood.

Elysia Walker and Dr Emily Doe, from the University of Buckingham, presented their findings yesterday at the annual conference of the British Psychological Society’s Division of Health Psychology.

Miss Walker said "this was a very middle-class sample", adding that further research was necessary to see whether there was a similar link in different social classes.