Objective To examine the impact of the ban on smoking in enclosed public places implemented in England in July 2007 on children's exposure to secondhand tobacco smoke.

Design Repeated cross-sectional surveys of the general population in England.

Setting The Health Survey for England.

Participants Confirmed non-smoking children aged 4–15 with measured saliva cotinine participating in surveys from 1998 to 2008, a total of 10 825 children across years.

Main outcome measures The proportion of children living in homes reported to be smoke-free; the proportion of children with undetectable concentrations of cotinine; geometric mean cotinine as an objective indicator of overall exposure.

Results Significantly more children with smoking parents lived in smoke-free homes in 2008 (48.1%, 95% CI 43.0% to 53.1%) than in either 2006 (35.5%, 95% CI 29.7% to 41.7%) or the first 6 months of 2007, immediately before the ban came into effect (30.5%, 95% CI 19.7% to 43.9%). A total of 41.1% (95% CI 38.9% to 43.4%) of children had undetectable cotinine in 2008, up from 34.0% (95% CI 30.8% to 37.3%) in 2006. Geometric mean cotinine in all children combined was 0.21 ng/ml (95% CI 0.20 to 0.23) in 2008, slightly lower than in 2006, 0.24 ng/ml (95% CI 0.21 to 0.26).

Conclusions Predictions that the 2007 legislative ban on smoking in enclosed public places would adversely affect children's exposure to tobacco smoke were not confirmed. While overall exposure in children has not been greatly affected by the ban, the trend towards the adoption of smoke-free homes by parents who themselves smoke has received fresh impetus.