The announcement comes on No Smoking Day, just after Chancellor Gordon Brown added 17.5p to the price of a packet of 20 cigarettes.

While it has been long been taken for granted that pricing has an effect on adult behaviour, no-one has looked at how it influences children.

The new study, backed by the Cancer Research Campaign, will quiz 2,500 children aged between 12 and 14 from 23 schools.

More children taking up the habit

The Cancer Research Campaign says more children are starting to smoke than adults. It said the proportion of children aged 11-15 who regularly smoke has increased from 8% in 1988 to 13% in 1996.

Dr Andrew Povey, of Manchester University, is co-ordinating the project.

He said: "This is the first time a major research project has been carried out in Britain to find out whether price rises deter children from smoking.

"We already know a lot about what influences children to start smoking, such as peer pressure, but now we need to know the factors that will make them stop."

Government targets

Girls smoke more than boys

The CRC says while few children under the age of 12 smoke, by 15 more than one in four are regular smokers.

Because most adult smokers start during childhood, adolescent years are the most important time to tackle the issue, it says.

The government's White Paper, Smoking Kills, published last year, set a target of reducing smoking among children from 13% to 9% by the year 2010.

Emeritus Fellow Professor Anne Charlton, the project adviser, said: "If the study shows that British children are price sensitive, we will be able to tell the government what level of tax increase would be most effective in deterring young smokers.

"If, on the other hand, British children are not price sensitive, I hope our survey will tell us why they are not, so both we and the government know where best to targetr resources to prevent children from smoking."

Researchers launched the study a week before the government's price increase on 1 December last year when 21p was added to a packet of 20 cigarettes.

This meant children's smoking habits could be gauged in a detailed questionnaire completed before and after the price hike.

The results from these two surveys are being analysed and a final questionnaire will be given to the chidren in May to see if the effects of the price increase are long term.

The eight-page questionnaire will investigate the children's smoking behaviour as well as the differences between boys and girls, family factors, social background and the children's reasons for smoking.