A GIANT "prescription" calling on the Government to ban smoking in the workplace was signed by doctors yesterday as it emerged Labour was considering making the pledge in its election manifesto.

Delegates at the British Medical Association's conference also heard that 4,500 letters from doctors, concerned about the health effects of tobacco, would to be sent to the Prime Minister.

News of the Labour Party's proposal came in a leaked document as research found that the dangers of passive smoking could be even greater than previously estimated.

Earlier this month, the BMA urged 1,000 doctors to write to Tony Blair urging him to end passive smoking with a ban in workplaces including pubs and restaurants.

But by the end of the month it had received 4,500 letters.

Dr Peter Maguire, deputy chairman of the BMA board of science, led calls for the Government to follow the lead of countries such as Ireland and Norway.

"I live in Northern Ireland and yet I travel down to the Republic because I know that's where I have the choice to enjoy a beer in a smoke-free pub," he said.

"I have seen that the ban on smoking in public places in Ireland has not affected business - business is booming there.

"Smoke-free places mean life not death."

The possibility of giving local authorities powers to introduce bans at work and in public places was a key theme of the Government's public consultation exercise - the Big Conversation - carried out over the past few months.

The leaked policy document is the first indication of the outcome of the exercise and will be discussed by Labour's Policy Forum next month.

Alongside smoking restrictions, the document discusses measures to clamp down on binge-drinking and unscrupulous food marketing.

It discusses the possibility of sustained above-inflation increases in tobacco taxes as a means of cutting cigarette consumption, and notes that it would be necessary to decide whether a ban should be imposed by local or national government.

A Labour spokesman said: "The draft document reflects the concerns raised by party members on this issue, but does not draw definitive conclusions."

It came after a study claimed that the risks of heart disease faced by passive smokers were double what was previously estimated. It found that non-smokers faced a 50 to 60 per cent increased risk of falling victim to the disease.

Delegates voted overwhelmingly in favour of a motion calling on the BMA to lobby for the immediate introduction of a UK public smoking ban.

James Johnson, chairman of the BMA, said: "Smoke-free public places protect non-smokers."