Money worries and the distractions of social media mean people are having sex less frequently, researchers say.
A once-a-decade poll of 15,000 Britons found those aged 16-44 were having sex fewer than five times a month.
The figure compared with more than six times a month on the last two occasions when the official National Survey of Sexual Attitudes and Lifestyles was carried out, in 1990-91 and 1999-2001.
The study's authors say modern life may be having an impact on libidos.
Dr Cath Mercer, from University College London, said: "People are worried about their jobs, worried about money. They are not in the mood for sex.
"But we also think modern technologies are behind the trend too. People have tablets and smartphones and they are taking them into the bedroom, using Twitter and Facebook, answering emails."
She also said the survey suggested that couples aged 16 to 44 may be using online porn as a substitute for sex.
Men polled in 2010 to 2012 reported having sex 4.9 times a month and women 4.8. In both previous surveys the averages were more than six for both sexes both times.
The survey carried out by NatCen Social Research and analysed by researchers from University College London and the London School of Hygiene and Tropical Medicine also asked older people about their sex lives.
It found 42% of women and 60% of men aged 65 to 74 had had sex in the past year.
Nonetheless, they were the age groups having the least sex - 2.3 times a month for men and 1.4 for women.
Among men, the 25-to-34 age group were having the most sex - 5.4 times a month - and for women it was the 16-to-24 age group, 5.8 times.
The latest survey, which is carried out every 10 years, also shows the age at which people start having sex is lower in the younger age groups.
The average age for the under-25s is 16 compared with 19 for men and 18 for women in the 65-to-74 age group.
Among other findings:
One in six pregnancies in the UK is unplanned.
About half of men and women have had a recent sexual problem, but only a 10th of those interviewed were distressed or worried about their sex lives.
Lack of interest in sex is one of the most commonly reported problems, and one not confined to women - around 15% of men had experienced loss of libido.
Since the last survey in 2000 people have become more accepting of same-sex relationships but less tolerant of cheating spouses. For more about how attitudes have changed read more here.
The average woman aged under 44 said they had had 7.7 partners over their lifetime, while for men it was 11.7.
Some 3.6% of men had paid for sex in the last five years. Hardly any women had.
Genevieve Edwards, from Marie Stopes International, said: "A key insight from the survey is that people are having sex earlier and having children later, which means that, on average, women in Britain spend about 30 years of their life needing to avert an unplanned pregnancy, yet many are not being informed about or offered the full range of services.
"Long-acting contraceptives, for example, can be extremely effective and convenient but too many are never offered the choice."
But the poll - the full details of which have been reported in the Lancet - also revealed the extent to which people are forced to have sex against their will.
One in 10 women and one in 70 men said they had experienced it.
However, fewer than half had told anyone about it and even fewer (13% of women and 8% of men) had reported the crime to the police.
11月26日发布的一项调查研究全面展现了过去10年来英国人的性生活状况。调查结果显示，英国人现在担心工作，关注社交媒体，性生活相应减少。另外，有40%的女性曾被迫和伴侣发生性行为。
2010年9月至2012年8月间，英国 伦敦学院大学、国家社会研究中心、以及伦敦卫生和热带医药学院联合对1.5万多名16岁至74岁的英国民众进行《全国性态度和生活方式调查》 (Nastal)，得出上述结论。该调查如今已经进行到第三届，前两届分别是1990年2000年。
据英国广播公司报道，调查显示，年龄在 16岁至44岁之间的英国人每个月性生活不到5次，低于前两届的6次以上。伦敦学院大学的卡斯•默瑟博士说：“人们担心工作担心钱，没心情做爱。我们觉得 现代科技也有影响。大家都有平板电脑和智能手机，还把它们带进卧室，浏览社交网站，回复电子邮件。”默瑟还透露说，人们可能浏览色情网页，补充真实的性生 活。
男性在25岁至34岁间的性生活最为丰 富，每个月平均5.4次；女性在16岁至24岁间最多，为5.8次。在65岁到74岁年龄段中，男女每个月性行为次数分别为2.3次和1.4次。大约有一 半受访者近期在性生活方面遇到问题，但并不担心。男性和女性都存在性欲不足的情况。另外，调查之前5年内，有3.6%的男性曾花钱买春，女性则几乎没有。
英国《独立报》报道，调查显示1.5万名 女性受访者中有40%表示曾被迫和前任或现任伴侣发生性关系，这些受害者的平均年龄为18岁。相对而言，只有73名男性在“13岁以后被迫与他人发生性关 系”。研究人员温迪•麦克道尔认为，被迫性行为已经“正常化”，它的极端形式就是强奸。
伦敦卫生和热带医药学院的凯•韦林斯教授 说：“Nastal等研究表明，民众的性行为在过去一个世纪发生了深远变化。初次性体验提前，性生活活跃的长者数量增加，男女之间差距缩小，而性行为和生 育之间的联系有所减弱。我们要在研究、临床实践和教育方面应对这些变化。我们需要换个视角看待性。性健康不仅仅代表不生病，还要给人带来愉快、安全、不受 胁迫的性体验。”