(CNN) Couples are having less sex than in the previous two decades, new UK research says -- but the number of people wanting more is rising.

A survey found that British people who are married or living with a partner are having sex less often, driving an overall decline in sex within UK society. People over the age of 25 are also having less sex, while more than half of British women and almost two-thirds of men admitted wanting more.

But the general declines did not apply as much to single people, and men under the age of 25 bucked the societal trend and did not report a dropoff in their sex lives. Only 43.4% of single men reported no sex in the previous month in 2012, compared with 50.3% in 1991.

Researchers at the London School of Hygiene and Tropical Medicine analyzed data on more than 34,000 people aged 16 to 44 who had completed the National Survey of Sexual Attitudes and Lifestyles in 1991, 2001 and 2012. Both opposite-sex and same-sex intercourse were included.

There was a significant increase in people overall reporting not having had sex in the previous month between 2001 and 2012; for men, the number jumped from 26% to 29.2%, and for women, it rose from 23% to 29.3%.

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