For a major new study shows that nicotine addicts driven from bars and restaurants will light up more often at home - increasing the effects of passive smoking on their children.

The study, hotly disputed last night by a local cancer expert, was carried out by Francesca Conaglia and Jerome Adda of University College London.

They examined the relative effects of smoking bans in various states of the US and found the group most affected by changes in regulations were children.

And they concluded that it led to an increase in the levels of cotinine - a substance that indicates how much exposure to tobacco smoke someone has had - in children whose parents smoke.

The study also found that children in smoking households had higher levels of cotinine during winter periods.

Said the authors: "We find no seasonal effects for children living in non-smoking households.

"It is consistent with a displacement effect, where adult smokers chose to smoke at home instead of in bars or restaurants."

They added: "Our results question the usefulness of bans in reducing smoking exposure for non-smokers.

"Displacing smoking towards places where non-smokers live is particularly inefficient. Therefore, total bans may not be the optimal policy."

The findings were welcomed by a spokesman for smokers' rights group FOREST, who said the Government was warned that a comprehensive ban would mean greater exposure for children.

But Gerry McElwee, head of cancer prevention at the Ulster Cancer Society, said there were other studies that showed exactly the opposite.

"Evidence from some studies in America and New Zealand show that, when people stop smoking in the workplace, they also stop smoking at home," he said.

"We don't tolerate asbestos nowadays and it's illogical we should in the 21st century allow people to be exposed to something that kills them."

But Mr McElwee believes that a smoke-free policy alone will not dramatically reduce the number of lung cancer deaths - around 800 annually - in the province.

"We need a comprehensive package, because smoking is ingrained in our society," he added.

"It will take a lot to eradicate it and legislators will have to be reminded of the need for policies on pricing and advertising.

"In the south of Ireland, there has not been an increase in tobacco in the last four or five budgets, so in real terms, tobacco prices have fallen."

slnews@belfasttelegraph.co.uk