Casual sex is rife among British young people, who are putting their health at risk by not using condoms with new partners, according to a new survey.
The study also found that nearly a third of 16 to 24 year olds lost their virginity before the age of consent.
And a large number of young people do not always use a condom with a new partner, with the most common reason given being that the girl is on the pill - which offers no protection against s exually transmitted infections. The second most common reason was being too drunk.
The survey, BareAll06, of nearly 20,000 16-24 year-olds was conducted by its partners BBC Radio 1, 1Xtra, MTV and Durex, and supported by the Department of Health.
Sam Steele, BBC Radio 1's executive producer of Speech and Campaigns said: "Overall, our results have shown that young people are informed about methods of contraception, but they simply aren't using their knowledge.
"Together with 1Xtra, MTV, Durex and with the support of the DoH, we have both the ability to engage with a significant proportion of young people in the UK and deep insights with which to empower our audience to use their knowledge."
Michael Barry, managing director MTV Networks UK & Ireland, said: "There are lots of stereotypes about what young people think about sex, what they get up to behind closed doors and whether safe sex messages are cutting through.
"Rather than make blind assumptions, we wanted to find out the truth to share with our viewers. BareAll06 is by far the most extensive survey of its kind."
Martyn Ward, managing director of Durex UK, said: "These findings show there is still the need to emphasise the dangers of unprotected sex and particularly the importance of using a condom during sex, as a condom is the only method of stopping the spread of sexually transmitted infections and preventing unplanned pregnancy."
Health Minister Norman Warner said: "This survey provides a valuable picture of the attitudes and views of young people on sex.
"It is encouraging that young people are confident to talk about using contraception, but to tackle the number of STIs, we have to get them to use condoms more in their sexual encounters. This is why our new sexual health campaign will be aimed at normalising condom use.
"We want to make sure we're listening to what young people have to say, and today's survey will help us give them the information they need."
* 19,250 young people aged 16 to 24 took part in the survey from May 22 to July 21 this year
* It found nearly a third of 16 to 24-year-olds (30 per cent) lost their virginity before the age of consent and 38 per cent in that age bracket do not always use a condom with a new partner
* The most common reason (44 per cent) is because the girl is on the pill, the second most common reason (17 per cent) was being too drunk
* Respondents from Wales and the South-west tend to lose their virginity earlier, with 32 per cent losing it before the age of 16.
* More than half - 57 per cent - of respondents have had a one night stand. However, 23 per cent would never have one n Some 43 per cent of 16-24 year-olds have had at least five sexual partners, while 18 per cent have had ten or more
* Pregnancy is the biggest worry among the age group regarding sex - 41 per cent of respondents chose it as their main concern. That was nearly double the proportion concerned with catching HIV or a sexually transmitted infection