Raising the legal age of smoking to 21 or even would dramatically slash the numbers of teenagers taking up the deadly habit, researchers said.
Until 2007 British teenagers could buy cigarettes and tobacco when aged 16 but in that year this was increased to 18.
But Canadian scientists said raising it to 21 would see a quarter less smokers and urged lawmakers to change the rules to stop needless deaths and illnesses.
The call was made as new guidelines were introduced to help children as young as five quit by encouraging family doctors to take a more active role.
Nearly a fifth - 18 per cent - of children aged 11 to 18 had tried smoking but those experimenting increases with age.
Only three per cent of 11-year-old tried smoking but over a third - 36 per cent - of those aged 17 to 18 had.
And nine out of ten current smokers said they had tried smoking before they were 18.
Assistant Professor Dr John Oyston at the University of Toronto and Scarborough Rouge Hospital pointed out as the dangers of tobacco has become known, cigarette advertising and smoking in public places has been banned.
He said: “Now that we know that the addictive substance nicotine is a neurotoxin
that damages the developing brain, from foetal life to young adulthood, a new measure is needed to protect young people from tobacco.
“Increasing the minimum legal age for access to tobacco products to 21 or even 25 years would reduce smoking initiation substantially, reduce the prevalence of smoking, improve health across the lifespan, improve the outcome of many teenage pregnancies and save lives.”
He said if a man has never smoked by age 18, the odds are three-to-one he never will and by 24 the odds are twenty-to-one.
But he added: “Teenagers typically exhibit risk-taking behaviour because the prefrontal cortex, needed for planning and impulse control, does not fully mature until about age 25 years.”
Currently 201 000 teenagers aged 15 to 19 years smoke and three quarters will continue as adults.
Yet the earlier a child starts, the more they smoke over a longer period and find to hard to stub out the habit.
Half of those will die early because of smoking.
He noted when Needham in Massachusetts raised the legal age to 21, smoking rates declined 47 per cent in high schools students.
In Canada the federal minimum age is 18 but in the six Canadian provinces where it was raised to 19, the numbers of smokers reduced from 14.8 per cent to 11.7 per cent.
Critics of changing the law argue underage smokers do so before they can legally buy tobacco products but he said many get them from older friends or siblings.
Raising the age limit will stop these older smokers buying them legally.
Others argue 18-year-olds are adults and can enlist in the armed forces but he countered “smoking is more deadly” and serving Queen and country “has benefits both to the individual and to society.
“Smoking benefits no one.
“As physicians, we should spare no effort in preventing young people from starting to smoke.
“Eighteen or 19 is too young to be allowed legal access to an addictive and carcinogenic product that can never be used safely.
“Raising the minimum legal age for access to tobacco is a scientifically proven, legally and politically feasible, quick, cheap and effective way to deprive the tobacco industry of recruiting a new generation of young people as their customers.”
Dr Brett Thombs, chair of the Canadian Task Force on Preventive Health Care which issued its first ever guideline said GPs need to intervene earlier to nip teen smoking in the bud.
Smoking by children and teenagers “is a potentially reversible driver of disease in adulthood” so doctors should question children and parents about their smoking.
He said: “The evidence suggests that low-intensity behavioural interventions based on providing brief information and advice may help to prevent and treat tobacco smoking among children and youth.
“The task force therefore recommends that primary care practitioners consider offering such interventions to children and youth aged five to 18 years.”
The guidelines and commentary were published in the Canadian Medical Association Journal.