More than two-thirds of young people still wait until at least the age of consent before losing their virginity, Britain's largest sex survey reveals today.

In a finding that suggests Britain's teenagers may be more cautious than previously suspected, seven out of 10 (69%) 16- to 24-year-olds said they waited until 16 or over before having sex. Almost a quarter (23%) first had sex at 16, but nearly half (46%) waited until they were older.

The survey, BareAll06, an online poll supported by the Department of Health and answered by nearly 20,000 young people, shows that 60% of young people aged 22 to 24 had had more than five sexual partners, compared with 23% of 16- to 18-year-olds. One in five (18%) said they had slept with 10 partners or more.

More than half - 57% - claimed to have had a one-night stand, with only a fifth ruling out ever doing so. But, despite Britain having the highest incidence of sexually transmitted infections (STIs) in western Europe, 38% of 16- to 24-year-olds did not always use a condom with a new partner. A quarter (24%) used no contraception the first time they had sex, while one in 10 routinely used nothing or relied on withdrawal. Being on the pill was cited as the main reason for not using condoms, but 17% cited being "too drunk" - the second most common reason.

The survey, conducted jointly by Radio 1, the BBC's black music station 1Xtra, MTV and Durex, also indicates alarming gaps in sex education. One in 10 claimed to have had no sex education in school, while the vast majority (79%) learned only the basics. The government requires secondary schools to teach only basic reproduction. School governors decide on further sex education, and parents who disapprove can opt for their children to miss lessons. Pupils in private schools need receive no sex education at all.

Sam Steele, 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."

Campaigners say the findings show young people need compulsory sex education so they know the health risks associated with having multiple partners.

A spokeswoman for Brook, the national sexual health charity for young people, said: "Brook is calling for sex and relationships education to be made a compulsory part of the national curriculum so that every young person is guaranteed to receive the information they need to protect themselves."

The public health minister, Lord Warner, said: "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."

The Department of Health said the government was trying to improve sex education through its RUThinking campaign, which aims to reduce the number of teenage pregnancies. The government has set a target of halving teenage pregnancies by 2010 but they have fallen by only 11% since 1998 and remain the highest in western Europe.

One of the survey's few positive findings was that pressure to have sex appears to be declining, with significantly fewer women aged under 18 feeling pressured compared with those aged 32 or over (23% against 33%). Nearly 10,000 24- to 34-year-olds also took part in the survey.

Other findings revealed that only 4% of those aged 24 or under were virgins, with those from Wales and the south-west losing their virginity earliest.

Vicky Field, policy officer of the Terrence Higgins Trust, said: "Despite the continued rise in sexually transmitted infections, safer sex messages just aren't getting through to young people. We need sex and relationships education to move beyond just biology. It should cover the risks of unprotected sex, the importance of condoms and how to negotiate condom use with your partner."