The number of teenagers in England who smoke has fallen since the legal tobacco-purchase age was raised from 16 to 18, academics claim.
Staff at University College London surveyed around 1,000 people aged 16-17 before and after the legal age was changed in October 2007.
Before October 2007, a quarter of the respondents (24%) said they smoked. After the law was changed around 17% admitted to smoking. The proportion of over-18s who said they smoked was the same.
Cancer Research UK, which was involved in the study at its health behaviour research centre at UCL, claimed the poll findings showed that the law can influence levels of young smokers.
It is known that at least eight in 10 smokers took up the habit before they were 19 years old, and that cancer or another tobacco-related disease will kill half of all long-term smokers.
Not starting smoking is key to reducing the huge number of people killed every year by tobacco products, the charity said.
Research leader Jenny Fidler, whose survey results appeared in the Addiction journal, said: "The new law looks to have helped reduce smoking prevalence among younger age groups. This is good news for the future health of this generation of young people and shows that tobacco policies can make a real difference."