Significantly fewer children have been taken to hospital with symptoms of asthma since the ban on smoking in public places came into force, according to researchers at Imperial College London.
In the first year from July 2007 there was a 12.3% fall in admissions. The figure continued to drop in subsequent years - the equivalent to 6,802 fewer hospital admissions in the first three years.
Dr Christopher Millett of Imperial College London said: "Previous studies have also suggested that the smoke-free law changed people's attitudes about exposing others to second-hand smoke and led more people to abstain from smoking voluntarily at home and in cars.
"We think that exposing children to less second-hand smoke in these settings probably played an important role in reducing asthma attacks. The findings are good news for England, and they should encourage countries where public smoking is permitted to consider introducing similar legislation."