Men have twice as many sexual partners as women over the course of their lives, research suggests.
The Health Survey for England found that men reported having 9.3 different partners on average, with a quarter of men boasting of more than 10 conquests.
However a third of those questioned admitted they were only estimating the number of notches on their bedposts.
By contrast, women had a mean average of 4.7 sexual partners in their lives so far, with a quarter having just one. They were more likely to be certain of the number of lovers they had had.
Among older women, monogamy was even more common with 40 percent of those aged between 55 and 69 saying they had only ever had one sexual partner.
Older women were also far less likely to be sexually active, with 36 percent saying they had not had a partner in the past year. Overall a fifth of respondents aged between 16 and 69 had been chaste.
The poll of 14,000 people, published by the NHS Information Centre on Thursday, suggested that younger generations were losing their virginity at ever earlier ages and taking more risks.
Its chief executive Tim Straughan said the annual report, which asked questions about sex for the first time, "paints a picture of sexual behaviour which is changing over the generations with younger women tending to begin having sex younger".
A fifth of men and one in seven women said they had had sex before their sixteenth birthday, and the median age for first sex was 17. Overall fewer than one in 10 of those questioned were still virgins.
But among 16 to 24 year-old women the proportion who had lost their virginity before 16 – which would mean their partners were breaking the law – rose to 27 percent.
In addition, 15 percent of young women had had between two and four different sexual partners in the past year.
The Public Health Minister, Anne Milton, said: “Young people should think carefully before having sex - it's not something to rush into. Consider seriously if it's right for you, what contraception to use and the best way to protect yourself from sexually transmitted infections.”