Speaking on the third day of the British Medical Association's Annual Representative Meeting in Belfast, they called for action to tackle public health problems.

Dr Nigel Vetter, a public health doctor in Cardiff, said people smoking on the street were setting a bad example.

"We've tried for years to stop people smoking and its our children who aren't listening," he said.

"I have 15-year-old daughter - she never listens to me except on smoking."

He said this was because he did not smoke, and that if fewer people were seen smoking, fewer children would be tempted to take up the habit.

Underage smokers spent £135m a year on tobacco, he said.

"£105m of that goes straight to the government - the government is living off immoral earnings," he said.

Dr Jonathan Reggler, a GP from Marlow in Buckinghamshire, spoke against the ban, although he said he supported the principle of reducing smoking.

He said the idea of banning smoking in "public places" was too vague and would require "extraordinary legislation".

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Alcohol can damage health

The conference also called for legislation to ban cinema advertisements for alcohol being shown to under 18s

Dr Martin Breach, a specialist registrar in Northern Ireland and member of the BMA council, said alcohol advertisers were not supposed to target children, but used the cinema as a get out.

He said the atmosphere of the cinema took people into a fantasy world, where they were more open to suggestion, particularly children.

"Evidence has shown that adverts have little effect on the drinking habits of adults, but it has been shown to influence the future drinking habits of younger people," he said.

And Professor Sir William Asscher, chairman of the BMA's board of science and education, pointed to a recent report from the association.