ObjectiveTo examine the changes in the prevalence of, and the factors associated with, the use of emergency contraception (EC) in Britain between 2000 and 2010, spanning the period of deregulation and increase in pharmacy supply. DesignCross-sectional probability sample surveys. Setting and populationBritish general population. MethodsData were analysed from the second and third British National Surveys of Sexual Attitudes and Lifestyles (Natsal), undertaken in 1999-2001 and 2010-12. Univariate and logistic regression analyses were used to measure change in EC use amongst sexually active women aged 16-44years not intending pregnancy. Main outcome measuresPrevalence of EC use and factors associated with use. ResultsOf the 5430 women surveyed in 1999-2001 and the 4825 women surveyed in 2010-12, 2.3 and 3.6%, respectively, reported using EC in the year prior to interview (P=0.0019 for change over time). The prevalence of EC use increased amongst single women and those with higher educational attainment (adjusted odds ratio, aOR1.51; 95% confidence interval, 95%CI 1.04-2.20; P=0.0308). Increases in EC use were generally greater among women without behavioural risk factors, such as those with no history of abortion within 5years (aOR1.57; 95%CI 1.17-2.12; P=0.0029), or those whose first heterosexual intercourse occurred after the age of 16years (aOR1.68; 95%CI 1.21-2.35; P=0.0021). The increase in EC use was also more marked among women usually accessing contraception from retail sources than among those doing so from healthcare sources, which may reflect a use of condoms amongst EC users. ConclusionThe increase in EC use among women in Britain in the first decade of the 21st century was associated with some, but not all, risk factors for unplanned pregnancy. Advice and provision may need to be targeted at those at highest risk of unplanned pregnancy. Tweetable abstractDespite pharmacy access, only a small rise in emergency contraception use has been seen in Britain over 10years. Tweetable abstract Despite pharmacy access, only a small rise in emergency contraception use has been seen in Britain over 10years.