Widespread ignorance of sexually transmitted diseases is contributing to a growing crisis in sexual health, according to a report.
Many people fail to have safe sex
The Family Planning Association (FPA) found that despite repeating public health campaigns, many people were still failing to use condoms.
It is calling for the government to introduce a national screening programme for chlamydia - the most commonly diagnosed STD in 2002 - as soon as possible.
Rates of chlamydia are highest in 16-24 year old men and women, yet when questioned, just over 60% of this group in a sexual relationship admitted they had never, or only sometimes, used a condom in the previous year.
This is despite the fact that over a quarter of them had two or three sexual partners during this time.
Chlamydia is sometimes called the 'silent infection' as it shows no symptoms in 70% of women and 50% of men, but if left untreated can cause infertility.
Over 81,000 cases were diagnosed in 2002 at genitourinary medicine clinics - an increase of 139% since 1996.
In 1999 pilot studies for the screening programme in Portsmouth and the Wirral found one in 10 young women under 25 tested positive for chlamydia.
The FPA survey found 59% of people in a relationship said they had talked to their partner about past sexual history before having sex.
But 58% also said they had not used a condom in the previous year.
Anne Weyman, FPA chief executive said: "Opportunistic screening for chlamydia in women under 25 years is a must.
"Yet the screening programme has been delayed due to a lack of significant and sustained investment.
"This is a crazy, false economy on the part of the government considering that dealing with the consequences of untreated chlamydia, such as ectopic pregnancy, pelvic inflammatory disease and fertility problems costs the NHS an estimated £50m a year."
The Royal College of Nursing (RCN) backed the call for a national chlamydia screening programme.
Beverly Malone, RCN general secretary, said extra funding was also required to boost sexual health services.
"Patients require access to care at the earliest possible opportunity yet the current system means they suffer delays due to an overburdened service.
"Chlamydia like many other sexual infections is a condition that can be easily treated but has dire consequence if not. Under-funding of sexual health services is putting patients at risk."
Nuala Scarisbrick, of the pro-life group Life, said making condoms more available and sex education more explicit would not solve the problem.
"It is remarkable these so-called `family planning experts' never suggest young people should not be having sex in the first place.
"Youngsters are being let down badly. By failing to protect and nurture them, we are exposing them to sexual knowledge that they should be unaware of until
they are much older, and exposing them to diseases which could ruin the rest of
The Department of Health said the size of the pilot chlamydia screening programme was to be doubled later this year.
In addition, screening was already on offer in various places around the country.
A spokesman said: "Reducing transmission of STIs is a complex issue that will involve people in changing their behaviour.
"There is no quick fix but the NHS is working to reverse the upward trends in infections, tackling inequalities and modernising services."