Two-thirds of sexually active students have had unprotected sex, a new survey reveals.

The StudentBeans website surveyed more than 5,000 young people at UK universities about their sex lives and sexual health. They answered questions on their use of contraception, whether or not they had had a sexually transmitted infection, and their experiences of sex education.

Of those with sexual experience (89% of the respondents), two-thirds had had unprotected sex. Only 27% of sexually active students say they always use condoms, compared with 31% in last year's StudentBeans survey, while 35% use them sometimes and 26% just with a new partner.

The survey also found that more than two-fifths of students (45%) say they wish they'd had better sex education at school. One said: "Sex education at school was pretty awful. It was nearly all really basic biology stuff that we already knew and nothing about the relationship, trust or confidence side, which I think really could have helped. The boys never really took it seriously and, as a result, it became a bit of a weekly joke. The teacher didn't seem comfortable talking to us about it either, which didn't help."

Another student commented: "Sex education was utterly useless to me in a girls' school as a lesbian. I wasn't told anything about how to have safe sex or even what sexually transmited diseases it was possible for a lesbian to get – the idea some of us might not be completely heterosexual just wasn't entertained."

The survey asked where students first learned about "the facts of life"; 63% said in sex education classes at school, 34% said their parents, 36% said in the playground and 19% had looked online.

A quarter of those who responded said they would like to see more information on sexual health being offered at university.

The students were also asked where they would turn now for advice and information. Some 73% said their friends, 72% said they would look online and 19% would read magazines. Just over a third (34%) cited their GP, and 37% said a sexual health clinic.

Many of the students said that university life offered an opportunity to experiment sexually. One said: "It is a community of young people, all wanting to have that university experience, and sex and relationships is seen to be part of it."

Liam Burns, the NUS president, said student unions provide contraception and information, especially for freshers. "One potential issue is that local sexual health services can be overwhelmed when there are lots of students living nearby and it's important that these services are fit for purpose," he said.

"Sex education at schools is so focused on the experiences of heterosexual people that many young LGBT people can feel that they lack the information that they need."

The Department of Health declined to comment on the survey's findings, but the Department for Education said personal social and health education, which includes sex education, is being reviewed "to see how we can improve the quality of teaching".