England banned smoking in cars carrying children in 2015 and Scotland in 2016. With survey data from three years for both countries (NEngland=3,483-6,920,NScotland=232-319), we used this natural experiment to assess impacts of the English ban using logistic regression within a difference-in-differences framework. Among children aged 13-15 years, self-reported levels of regular exposure to smoke in cars were 3.4% in 2012, 2.2% in 2014 and 1.3% in 2016 for Scotland and 6.3%, 5.9% and 1.6% in England. The ban in England was associated with a -4.1% (95%CI -4.9%;-3.3%) absolute reduction (72% relative reduction) in exposure to tobacco smoke among children.