Couples are not as sexually active as they were a decade ago, experts have revealed, with digital distractions to blame.

More than 34,000 men and women aged 16 to 44 were analysed for the study, one of the largest sexual behaviour surveys in the world.

It found lovers spend too much time on Facebook, smartphones and watching Netflix box sets, with fewer than half being intimate at least once a week.

Declines in sex frequency were largest among those living together or married and those over 25.

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The study, published on Tuesday in the British Medical Journal, looked at surveys in 1991, 2001 and 2012.

It showed those married were having slightly more sex in 2001 than in 1991 but less in 2012 than in either of the previous years surveyed.

There has been a significant increase among both genders not having sex, with the study showing a 23 per cent to 29.3 per cent spike for women and 26 per cent to 29.2 per cent hike for men.

Lead author of the study — Britain's National Survey of Sexual Attitudes and Lifestyles — Kaye Wellings said digital devices and services were all "likely distractions that may prevent intimacy".

"Several factors are likely to explain the declines, but one may be the sheer pace of modern life," said Ms Wellings, a professor of sexual health at the London School of Hygiene & Tropical Medicine, in a statement.

While the study is UK specific, it does explain there has also been a decline in sexual frequency worldwide.

"Data from Australia, Finland, and the US are broadly consistent with our data, showing large declines in sex frequency among married people and those in early middle age," Wellings wrote.

Five years ago there was also a decline in Aussies having sex compared with the previous 10 years.

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According to the Australian Study of Health and Relationships, published in 2014, people in heterosexual relationships were having sex an average of 1.4 times per week, down from 1.8 times a week when the study was last conducted in 2003.

Wellings explained her study showed those most affected were middle-aged people.

"Men and women who, having started their families at older ages than previous generations, are often juggling childcare, work and responsibilities to parents who are getting older," she said.

The study suggested the decline in sexual frequency coincided with two events — the introduction of the iPhone in 2007 and the global recession of 2008.

"Others have suggested that increasing use of social media has resulted in increasing experience of 'virtual' as opposed to real-world sexual encounters, and the media have sometimes linked increasing use of pornography with decreasing frequency of partnered sex," the study noted.