The study found that among people in their 30s and 40s, and in partnerships where there is an age difference of five or more years, condom use is particularly low.
In view of the rising rates of sexually transmitted infections (STIs), the authors of the study say that condom use needs to be promoted to all age groups, and not just to young people.
The research has been published online in the International Journal of Epidemiology.
The research looks at all heterosexual relationships experienced in the
previous 12 months by 11,161 men and women interviewed for the second British National Survey of Sexual Attitudes and Lifestyles (Natsal 2).
Dr Catherine Mercer, a lecturer in the Centre for Sexual Health and HIV Research, University College London (UK), said: "To the best of our knowledge this is the first research to take account of all heterosexual partnerships and not just people's most recent partnerships, which tend to be more established partnerships such as marriages and cohabitations.
"Our study ensures accurate representation of casual partnerships, which are known to be important in the transmission of STIs. People with large numbers of partners contribute disproportionately to STI transmission in populations."
To reach the conclusion, Dr Mercer and her colleagues analysed data from interviews with 11,161 people, of whom 6,399 were women, carried out between May 1999 and February 2001.
Interviewees were asked about their three most recent partnerships, and the analysis focused on partnerships in the past year. Questions included ones on condom use, age differences in the partnership, where they met and how soon after meeting they had sex.
Of the 11,161 respondents, 9,598 reported a total of 15,488 heterosexual partnerships in the past year. A higher proportion of men's partnerships were described as "not regular" - 39.1 percent compared to 20 percent of women's partnerships; while a higher proportion of women's partnerships were marriages or cohabitations - 55.2 percent versus 38.9 percent of men's partnerships.
Men had sex sooner after first meeting a partner than women, with one in five men reporting sex within 24 hours of meeting their partner, compared with one in ten of women.
Condoms were used at last sex in 37.1 percent of men's and 28 percent of women's partnerships. Overall, half of all new partnerships involved condom use at first sex (55.3 percent), but this declined with age; for instance, 68 percent of men and 67.4 percent of women aged 16-19 used a condom at first sex, but only 38.1 percent of men and 28.8 percent of women aged 35-44 year-old did.
Dr Mercer said: "For some people not using condoms may be due to being or trying to become pregnant, but this is a less likely explanation for partnerships described as 'not regular', and it is therefore worrying that condom use was reported at last sex in just half of such partnerships.
"However, of greater concern was our finding that half of new partnerships did not use condoms at first sex, even when this was a non-regular partner, and condoms were not used in one-third of cases when first sex was within 24 hours of first meeting."