However, the idea does not meet with universal approval - even from anti-smoking campaigners.

The vaccine, reports New Scientist magazine, would work by blocking the pleasurable effect of nicotine on the brain.

It is this chemical which leads to tobacco addiction.

If you can take away the pleasure from the outset, children are more likely to kick the experiment early

John Roberts Xenova

Two pharmaceutical companies, Florida-based Nabi, and the UK's Xenova, are racing to produce a vaccine.

And both say it is possible that children could be vaccinated one day to prevent them picking up the habit in the first place.

John Roberts, Xenova's medical director, told New Scientist: "I think prevention offers a huge opportunity.

"If you can take away the pleasure from the outset, children are more likely to kick the experiment early.

"It normally takes several cigarettes to build up addiction."

Safety trials are underway on both vaccines, involving both smokers and non-smokers.

Mr Roberts said he was "very pleased" with results so far.

Immune response

The vaccines work by stimulating an immune response to nicotine molecules.

Normally nicotine is too small to produce such a response, but researchers have attached it to a large protein so that the immune system can recognise it.

This means that antibodies are launched to attack even normal nicotine molecules in the blood, hopefully wiping them out before they reach the brain.

An estimated 80% of smokers start in their teens, and the market potential of an effective vaccine is huge.

However, it is not clear whether regular boosters would be needed, or whether a few vaccinated patients would suffer more severe side-effects.

Opposition

However, even anti-smoking campaigners are luke-warm about the prospect of vaccination for non-smokers.

Clive Bates, from Action on Smoking and Health, said that civil liberties groups would be angered by the threat of "mass medication".

He said: "Things such as vaccines all carry risks. We need to walk before we can run, and help those people who are addicted to tobacco and trying to give up.

"Obviously, pharmaceutical companies are trying to find the biggest possible market for their product."