The most commonly diagnosed infection is genital warts, followed by herpes, the eight-year study found, with cases of chlamydia, herpes, warts, gonorrhoea and syphilis all rising sharply.

The widespread problem was put down to "sexual risk-taking" among older age groups by the study's authors.

"There has been a significant increase in the overall rate of STIs in older adults over the last few years, but little published research to inform public health policy, which remains youth focused," the authors wrote.

"The results of this study, together with evidence from a number of other studies, would indicate that sexual risk-taking behaviour is not confined to young people but also occurs among older people."

Julie Bentley, chief executive of FPA (formerly the Family Planning Association), said: "We've also noticed a rise in the numbers of over 45s phoning our helpline.

"Tragically, the sexual health of men and women of this age group is largely neglected and it's something FPA is increasingly concerned about.

"Services are geared towards young people, campaigns are targeted at the under 25s so over 45s think that sexual health has nothing to do with them and don't even know when they're taking risks.

"It isn't just young people who have sex. Fifty and 60 somethings (and older) are dating again and starting new
relationships.

"Once the worry of pregnancy goes away, it's easy to forget about sexually transmitted infections and the importance of using condoms.

"It's imperative that we move away from the equation that sexual health equals young people."

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