Health ministers are to ban the sale of tobacco to 16- and 17-year-olds from next year, changing a law that was put in place 70 years ago.

The Government will begin to "consult" next week on the ban, but privately the decision has already been taken to make it law.

It will mean that from 2007, a 17-year-old will be old enough in law to drive a car, fight in Iraq, have sex and get married - but too young to vote or buy alcohol or cigarettes.

The proposed ban has been given a lukewarm welcome by the main anti-smoking charity, ASH, who say its effect on tobacco addiction could be minimal.

But health professions worried by the prevalence of smoking about school age children say the ban should go ahead. The Roy Castle Lung Castle Foundation and the Trading Standards Institute have also backed the measure.

A report published this week by the British Medical Association in Scotland showed that even though smoking was decreasing faster in the UK than almost anywhere in the world, it was still true that 19 per cent of 15-years-olds and 6 per cent of 13-year-olds regularly smokes at least one cigarette a week. "A ban on sales will discourage teenagers from starting," one minister said.

Forest, the main organisation that campaigns for people's right to smoke, said it was not trying to prevent the ban from becoming law, though it warned that a law might put shopkeepers in a difficult position. "All the onus will be on the shopkeeper. The person who is selling tobacco will be breaking the law, but the person buying it won't be," it said.

The Labour MP Jeff Ennis, who campaigned to have the age limit raised, said: "It will actually make the lives of shopkeepers easier. It will mean a common age of sale for all the goods that are restricted - knives, alcohol and tobacco."