Scientists also found the sex habits of British women are changing faster than those of men, with a fourfold jump in the proportion of women who had a same-sex experience since the first survey was done in 1990, from 4 per cent to 16 per cent. In comparison, the numbers of men who reported a same-sex experience have remained virtually unchanged since 1990, at about 7 per cent.
On average, the number of sexual partners reported by women has doubled, from four to eight, whereas the number for men rose from nine to 12. The research also found an increasing sexual repertoire among both genders, with higher levels of anal and oral sex reported.
"It reflects a shift away from sex being seen purely in the context of reproduction toward a greater emphasis on pleasure and recreation," said Kaye Wellings, head of social and environmental health research at the London School of Hygiene and Tropical Medicine, one of the leaders of the research. She said similar results about changes in women's sex lives have been found in France.
The study found half of Britons reported having sex at least three times in the last month, versus five times when the first survey was done in 1990. Wellings noted that drop occurred at the same time as major changes in the use of technology and the financial crisis, which could interfere with a regular sex life.
"People are taking their iPhones and iPads into bed," she noted. "They're also working harder and maybe have less time for sex," she said.
Researchers also found half of Britons also lose their virginity by the time they were 17, about the same as 20 years ago. The study found people under 25 are at greatest risk of sexually transmitted infections and of being forced or coerced into sex.
The series of six papers were published online Tuesday in the journal, Lancet. Researchers interviewed more than 15,000 people aged 16 to 74 between 2010 and 2012 using in-person interviewers and a computer-assisted part for sensitive questions; no names of participants or other identifying details were shared. The studies were funded mostly by U.K. governmental groups and the Wellcome Trust.
Other scientists said the findings supported previous research that have found sexual orientation for women tends to be more fluid than for men.
"Women are more changeable in relation to social norms than men," said Cynthia Graham, a sex researcher at the University of Southampton, who was not part of the series. "Orientation isn't just gay, straight or bisexual," she said. "The boundaries are getting fuzzier."
Debra Lynne Herbenick, who led a survey on American sexual habits at Indiana University in 2009, said the findings in the U.K. were comparable to evolving attitudes in the U.S.
"There's been a relaxation of constraints on sexual expression," Herbenick said. "People are now more free to explore their sexual interests," she said.
Still, she said doubted current trends on increasing rates for certain kinds of sex would continue to increase indefinitely.
"Not everybody is going to want to do certain things, like have sex with somebody of the same sex," Herbenick said. "So there will be limits in terms of people's attractions."