Figures published on Tuesday will show sexually transmitted infections are on the increase.
Experts want to increase awareness of STIs
BBC News Online talks to doctors in genitourinary clinics about their battle to cope with the increasing number of patients.
"We'd always had a walk-in service, but about two to three years ago, we had to start turning people away," says Dr Phillip Hay, head of the Courtyard GUM clinic at St George's Hospital in London.
"It went completely against the grain, but we just didn't have the capacity to cope with demand.
"Since then, in line with other clinics, we have modified our practices so we can see more people. But we're faced with seeing 15 to 20% more people more each year."
The clinic now sees over 40,000 people a year. It has just four full-time consultants at St George's, and another four at other hospitals who see patients.
Dr Hay added: "We saw a big increase in the number of diagnoses of significant clamydia and gonorrhoea a couple of years ago. But at the moment, it's slightly lower than that.
"That might be because things have calmed down a little bit - or maybe those most at risk have stopped coming to see us."
Dr Hay said patients at the clinic are given advice about how to prevent themselves being infected again in the future - but it usually took a few visits before the message got through.
He said the key to reducing the numbers who need treatment at a GUM clinic is to educate people of the risk of STIs before they become infected.
"It's a question of getting the public health message across.
"Here, we're dealing with problems after they have happened. We're not getting people to think about the behaviour that's led to them getting an STI.
"There has to be a public health message before people come to us."
Dr Eric Monteiro, head of the GUM clinic at Leeds Teaching Hospital, said the rise in sexually transmitted infections was "quite clearly" due to changes in the sexual behaviour in the population.
He added: "The rate of partner change is greater; more people have sex at an earlier age. People having unprotected sex is also an issue.
"It may also be that the Aids epidemic warnings of the 1980s had some effect, and its worn off, although that is just conjecture."
The clinic has recently changed the way it books appointments to try and reduce its average of five hour waits. It is now introducing a system where patients have to phone in 48 hours ahead to secure an appointment.
Specialists there said they hoped the new system would enable them to reduce the amount of time people had to wait for appointments.
Dr Jan Clarke, a consultant in genitourinary medicine at the clinic, told BBC News Online: "We're dealing with acute infections, so it isn't logical for people to have to wait for that length of time."
She said it was crucial to make it as easy as possible for people - especially young people - to access services.
Dr Clarke said she hoped recent reports would raise awareness of the need to look after sexual health.
But if people couldn't access services, then it made it difficult to help them.
She added: "If people are infected, they haven't been able to get treatment and they haven't got a steady partner, they could be passing the infection on to others before they are seen."