Sexually active young people are facing a new scourge that has helped drive the epidemic of sexually transmitted infections to a 10- year high.

Cases of genital herpes rose 9 per cent last year, faster than any other sexual disease. Among teenage girls aged 16 to 19 the rise was even greater, at 16 per cent.

Genital herpes is caused by a virus and is incurable. The virus remains in the body for life and sufferers experience repeated recurrences, which can be severe. The increase pushed total cases of sexually transmitted infections up a further 2 per cent last year to 376,508. Britain has been in the grip of a 10-year epidemic that has seen infections rise by 63 per cent - almost 150,000 extra cases.

Casual sex, an increase in "risky behaviour" and a perception that the diseases are trivial has fuelled the rise. But public health experts said yesterday that there were signs the rise was slowing. Waiting lists for treatment at sexual- health clinics had fallen and there was evidence messages about safe sex were starting to get through.

Professor Pat Troop, the chief executive of the Health Protection Agency, which published the figures yesterday, said: "We have to tackle all the risky behaviours in a society where images involving alcohol, tobacco and sex bombard young people and don't make it easy for them. If you look at a lot of TV programmes, there is a lot of sexual behaviour and not a lot of thinking about safe sex. You don't see people in films pulling on a condom."

The explosion of infections over the past 10 years had been "very worrying" but there were now some "encouraging trends", with cases of gonorrhoea down for the third year running. "It is still very early and there is no room for complacency. The picture for young people and gay men remains particularly worrying," Professor Troop said.

Gwenda Hughes, the head of sexually transmitted infections at the agency, said that herpes and gonorrhoea affected different groups, which explained why one could rise while the other fell. Gonorrhoea - down from 25,000 cases in 2003 to 19,000 last year - was concentrated in urban populations among gay men and black ethnic populations, who could be targeted with awareness campaigns. Genital herpes - up from more than 19,000 to almost 22,000 in the same period - was distributed more widely, affecting rural communities as well, and was harder to tackle.

"If you can control gonorrhoea in the core group, you can have a major impact on the infection rate. That is harder to do for genital herpes," Ms Hughes said.

Genito-urinary clinics were under increasing pressure from the increased workload, up 6 per cent overall last year, but had cut waiting lists. Latest figures showed 85 per cent of patients were seen within 48 hours, according to the Department of Health, compared with less than 40 per cent in 2004.

A ten year epidemic

1996: 162 cases
2006: 2,766 cases
Increase: 1,607 per cent

1996: 13,063 cases
2006: 19,007 cases
Increase: 46 per cent

1996: 42.668 cases
2006: 113,585 cases
Increase: 166 per cent

1996: 16.615 cases
2006: 21,698 cases
Increase: 31 per cent

1996: 231,185
2006: 376,508
Increase: 63 per cent