British attitudes to sex – at least the ones they are willing to admit to – are changing, according to a new survey.

The National Survey of Sexual Attitudes and Lifestyles, conducted by researchers from three universities, a social research charity and a Government department, quizzed 15,000 British adults aged 16-74 about their sexual experiences through face-to-face interviews and an anonymous questionnaire about more sensitive topics.

The results of the survey, carried out between 2010 and 2012, allow social commentators to look at some of the more surprising trends to have emerged since the two previous surveys were conducted among people aged 16-44 in 1990-91 and 1990-2001. The results have been revealing.

Having been included in the survey for the first time, the results from the older generation flew in the face of common perceptions. Older people frequently continue to have sex into later life, with 42% of women and 60% of men aged 65-74 years having had at least one sexual partner in the previous year. However, the frequency and range of sexual practice – how many different types of sexual encounters older people have – decreases with age.

This may have something to do with general declines in health. Brits are known for being stoic when it comes to their health, but the survey suggests that people are beginning to seek help for health problems that affect their sex life.

Almost one in six people said they had a health condition that affected their sex life in the past year, yet fewer than one in four of these men and one in five of these women said that they had tried to get help or advice from a healthcare professional. Those who had were most likely to have talked to their GP.

The average number of sexual partners for men aged 16 to 44 dropped from 12.6 in the previous survey to 11.7 in the latest survey. But for women it went up from 6.5 to 7.7.

Overall, about 40% of people said they hadn't had sex recently (in the previous four weeks) and about 40% of people said they were dissatisfied with their sex life. People in poorer health were less likely to have had sex recently and less likely to say that they were satisfied.

People who hadn't had sex in the past year were more likely to say that they were dissatisfied with their sex life, and that they had avoided sex because of sexual difficulties (either theirs, or a partner's), compared with people who had had sex in the past year. However, only a minority of people who had not had sex in the past year said they were dissatisfied, distressed, or avoiding sex.

One theme of the survey is there is often a discrepancy between results from men and women. The researchers said there were various explanations for this, but some experts have suggested this can be explained by the different sexes being less than totally honest about their relationships.