The number of new cases of chlamydia has risen despite a Government campaign to stem the spread of the sexually transmitted infection, official figures revealed today.

The Health Protection Agency (HPA) reported an increase in the number of diagnoses of chlamydia from 121,791 in 2007 to 123,018 in 2008.

The number of cases stood at 113,713 in 2006.

Figures also showed a rise in the number of cases of genital warts and genital herpes at GUM (Genito-urinary medicine) clinics in the UK.

Genital wart infections rose by 3 per cent to 92,525 in 2008, up from 89,515 in 2007 and 83,616 in 2006.

Cases of genital herpes grew by 10 per cent, with 28,957 cases in 2008, compared with 26,270 in 2007 and 21,877 in 2006.

However, the HPA registered an 11 per cent decrease in the total new number of gonorrhoea infections with 16,629 in 2008, down from 18,649 in 2007 and 18,863 in 2006, the lowest number since 1999.

Syphilis also registered a 4 per cent decrease from 2,683 cases in 2006 and 2,633 in 2007 to 2,524 in 2008, but levels still remained "considerably higher" than a decade ago.

Overall, figures showed a slight increase in the total number of new STI infections, up 0.5 per cent from 397,909 cases in 2007, to 399,738 last year.

The HPA said young people age 16 to 24 continued to be "disproportionately affected" by STIs.

Only 12 per cent of the population are aged 16 to 24, but the age group accounted for more than half of all new STIs diagnosed in the UK.

Last year, 16 to 24-year-olds comprised 65 per cent of new chlamydia diagnoses (80,258 cases); 55 per cent of new genital warts diagnoses (51,153 cases); 47 per cent of new gonorrhoea diagnoses (8,605 cases); 44 per cent of new genital herpes diagnoses (12,258 cases) and 17 per cent of new syphilis diagnoses (456 cases).

Dr Gwenda Hughes, head of the Health Protection Agency's sexually transmitted infections department, said: "While the increase in genital herpes diagnoses in the last few years is probably due to greater use of highly sensitive tests detecting more cases, our data clearly show that considerable numbers of people, especially those under 25, are getting infected with an STI."

"Early detection is vital for both men and women as some infections, particularly chlamydia, gonorrhoea and genital herpes, can often have no symptoms.

"This means people may be unaware that they are infected and can pass the infection on to others. Without early treatment both chlamydia and gonorrhoea can lead to complications - when treatment can sometimes be too late to stop permanent damage such as infertility."