Health campaigns aimed at persuading teenagers not to smoke are not working, research has suggested.
Campaigners want more to be done to stop children smoking
A team from the University of Leeds looked at the smoking habits of teenagers over six years.
The study confirmed that teenage girls are twice as likely as boys to take up the habit.
Anti-smoking campaigners said population-wide measures, such as a ban on smoking in public places, were needed to cut teenage smoking rates.
This latest study involved 1,134 teenagers aged 15 to 16.
At age 11 to 12, just 2% of boys and 2% of girls had been regular smokers. But by the time they were 13 to 14, 16% of girls and 8% of boys were regular smokers.
And by age 15 to 16, 31% of girls and 16% of boys were smoking regularly.
The researchers used questionnaires, breath and saliva tests to assess the teenagers' smoking habits. The research was funded by the Economic and Social Research Council.
In an earlier study, beginning in 1998, more than 1,500
children at schools in the Leeds were monitored.
Half received lessons teaching them about the dangers of smoking and encouraging them to say "no" to cigarettes over two years.
It was found that this appeared to reduce the level of smoking among the younger students (11 to 12).
But when they returned two years later, the lessons appeared to have had
little lasting effect.
They said this emphasised the need to have repeated health education at
regular intervals if it was to have any long-term effect.
Adult rates falling
Dr Mark Conner, from the university's School of Psychology, said: "One suggestion [for the difference] is that it is something to do with teenage girls using tobacco as an appetite control mechanism. They are particularly using cigarettes to keep their weight down.
"But that is speculation and we are hoping to go back again and talk to those
who have smoked about their influences.
They found that just over half of the 15 to16-year-olds said they had not
had a puff of a cigarette in the past three months.
But that was less than at 13 to14, when 75% said they had not smoked in the previous three months.
Dr Conner said they were concerned by the increase in the number of teenage
smokers they found in their study.
"The figures are worryingly high. We have hoped that with adult smoking rates going down, the same would have been seen in teenagers."
Amanda Sandford, of Action on Smoking and Health, said: "The study shows that health education in itself is not enough to have a lasting effect on smoking rates.
"There needs to be more of a population-based approach. That includes a ban on tobacco advertising and on smoking in public places, plus more help for anyone who wants to quit smoking."
A Department of Health spokeswoman said: "We are aiming to create a climate where non-smoking is the norm, so there is less incentive for young people to take up the habit.
"The ban on advertising tobacco is aimed primarily at removing the attraction
of glossy advertisements which entice young people to try the product.
"Follow up regulations such as reducing the adverts on show in shops where
cigarettes are purchased are also designed to reduce the number of impulse buys
when young people decide to take up the habit.
"Over time we expect that the result will be a drop in take-up."