Young people who ignore the risks of unprotected sex are driving Britain's soaring rate of sexually transmitted infections, experts have warned.

More than 790,000 new diagnoses were made in genito-urinary medicine clinics in 2005, 3 per cent up on 2004 and almost 20 per cent higher than in 2001. Cases of chlamydia, herpes, genital warts and syphilis reached new highs, with syphilis showing the biggest increase.

Professor Peter Borriello, director of the centre for infections at the Health Protection Agency, said there was a tendency to treat sexually transmitted infections as trivial.

"[The attitude is] it's a dose of the clap, go and get an antibiotic, so what's the big deal?" he said. "The big deal is that chlamydia can make you sterile, syphilis can cause brain disease, human papilloma virus [genital warts] can cause [cervical] cancer and any infection can cause congenital malformations... We need to shatter the complacency."