Britain's "Frisky Fifties" have swapped the boardroom for the bedroom but one in 10 could be putting themselves at risk of infection by having sex without a contraceptive, a survey showed.

The survey of sexually active seniors in a youth dominated culture revealed age is no barrier for those with more time on their hands - almost half of those polled were having sex at least once a week.

"These findings shatter the myth that once you hit 50 your sex life is over," said Emma Soames, editor of Saga Magazine which has tapped a rich new market in sprightly, affluent pensioners ready to live their retirement years to the full.

By the year 2025, people over 60 will outnumber the under 25s in Britain. Already the over 55s, prime benefactors from a property boom, own 80 per cent of the nation's disposable wealth.

With the burden of bringing up children now lifted, many have money to burn while enjoying greater longevity and better health.

Soames said: "Forget about the Dirty Thirties or the Naughty Forties. The Frisky Fifties are having the most fun by swapping the boardroom for the bedroom".

Sex is also less pressure after 50, according to 85 per cent of those sounded out in the survey. Seven out of 10 found sex more fulfilling than when they did in their youth.

A minority of just 16 per cent admitted using performance enhancing drugs like Viagra for added zing.

"There is less pressure than when people were younger and it is likely that you feel more comfortable about your body," Soames said.

But the Populus survey of almost 8,000 over-50s did come with a health warning.

Recent research has shown increasing cases of sexually transmitted diseases in older age groups.

The survey showed that 12 per cent of sexually active over-50s do not use contraception with their current partner while also not knowing about their sexual history.

Soames said: "While a healthy sex life is a good thing, the over-50s must be wise to their sexual health as well as their overall health."