They found that teenagers whose parents and adult friends smoked were more likely to pick up the habit themselves.

Report author Professor Susan Woodruff, a professor at San Diego State University's Graduate School of Public Health, said their research showed that these children found it easier to get cigarettes and that this could be a reason for them smoking.

"Although it is important to continue to reduce commercial availability of tobacco to minors, these results suggest it is essential to develop strategies to decrease social availability, particularly from parents and other adults."

Cigarettes

Professor Woodruff and her colleagues studied nearly 500, non-smoking 12-15-year-olds, over a period of a year.

At the end of the study more than 6% of children admitted having tried cigarettes.

Further studies showed that these children were those who found it easy to get cigarettes from either parents or other adults.

These results suggest it is essential to develop strategies to decrease social availability, particularly from parents and other adults Professor Susan Woodruff

But Professor Woodruff said that most of the children involved said their parents would be upset that they had taken up smoking, suggesting that they were taking the cigarettes from them.

She said reducing access to cigarettes could have a great impact on the number of young smokers.

Retail

"These findings suggest that reducing social access and access at home may be important in controlling experimentation among younger adolescents.

"More in-depth surveys and formative research are needed to better understand the dynamics of adult and parent provision of cigarettes to adolescents.

"Social sources will likely become more important for underage smokers because of continuing retail price increases and increased retailer compliance with sales laws."

The report also revealed that the offer of cigarettes from friends and classmates was the strongest predictors of smoking.

But researchers said it was unclear whether this was because offers of cigarettes led to smoking, or whether those who had tried smoking were more likely to associate with other smokers.

The study results are published in the January/ February issue of the American Journal of Health Behaviour.