Figures released by the Health Protection Agency (HPA) show that a total of 482,696 new STI diagnoses were reported to the agency in 2009, up by nearly 12,000 on the 2008 total.

Of the total, 249,605 of the diagnoses were in men and 231,433 of the diagnoses were in women. In the remaining 1,658 cases the gender of the person being diagnosed was not reported.

Among women, around two-thirds of new STI diagnoses were in those under 25, while among men, more than half of new diagnoses were for those under 25.

Of the women diagnosed with Chlamydia 88 per cent were under 25.

The HPA said the high rates of STIs among young women was "in part due to more sensitive tests and community based testing targeting the under 25s in England".

Among men, 41 per cent of men diagnosed with gonorrhoea were under-25, as were 47 per cent of men diagnosed with genital warts, and 69 per cent of men diagnosed with Chlamydia.

According to the agency, the "peak age" for an STI in women is between the ages of 19 and 20 and between the ages of 20 and 23 in men. Around ten per cent of all 15- to 24-year-olds diagnosed with an STI last year will become re-infected within a year, the agency said.

Gwenda Hughes, head of the HPA's STI section, said: "These latest figures show that poor sexual health is a serious problem among the UK's young adults. Re-infection is also a worrying issue - the numbers we’re seeing in teenagers are of particular concern as this suggests teenagers are repeatedly putting their own, as well as others', long term health at risk from STIs."

In response to the figures Simon Blake, national director of charity Brook, called for the government to reconsider making sex and relationships education (SRE) statutory in all schools.

"The figures emphasise the urgent task of ensuring all young people have good quality education and services so they can make active decisions about sex that protect their physical and emotional health.   

"Young people tell us their SRE is too little, too late and too biological and it needs to address emotions and relationships more effectively. Done well, SRE provides an important antidote to the confusing sexual messages they receive in the playground and from the media day in day out. "