They say that although the treatment appears expensive in the short term, nicotine replacement therapy is a useful aid to giving up smoking.

It proves cost-effective because it is not a life-long treatment and can lead to a longer life, they said.

The therapy consists of administering nicotine in a variety of ways, including patches, chewing gum and sprays.

Most people who use it give up after about a month if it works for them.

'Quitting a priority'

Professor Godfrey Fowler, Emeritus Professor of General Practice at Oxford University and Dr Liam Smeeth, a GP at the department of primary care at London's Royal Free Hospital, made the claims in the British Medical Journal.

Professor Fowler is an ex-smoker who has advised the Department of Health's scientific committee on smoking policy.

He said he was interested in the issue because, although it was a long time ago, he remembered well the difficulty of giving up.

The doctors said the government's public health goals made reducing the number of smokers a priority.

"The World Health Organisation has identified smoking as the single most important preventable cause of death in Europe," they write.

They add, however, that "stopping smoking is difficult" and it is usually insufficient to simply advise someone to stop.

Limited power

Professor Fowler said: "A GP is denied something which he can offer people to help them, he is denied prescribing that for them on the health service.

"He isn't denied the right to give people tablets to help them sleep, tablets to deal with pain, even tablets to help them lose weight.

"But he isn't allowed the right to prescribe something to help them stop smoking."

Quitting can be hell

The doctors conducted a review of 47 trials of nicotine replacement therapy, involving 23,000 patients.

They found that the products doubled the success rate for those trying to give up smoking.

Professor Fowler said given the evidence, the therapy should be available on the NHS, because at the moment cost was a deterrent.

"I know people say, 'well, if you can afford to smoke you can afford to buy patches'," he said.

"But we don't apply that in other areas of health care - people who can afford to drink and run into alcohol problems get their care on the health service.

"If people over-eat they can get treatment, and now they're even thinking of giving people Viagra on the health service.

"Smoking kills one in five people in this country. It seems extraordinary that something that helps with that is not available on the NHS."

'Kick-start'

Action on Smoking and Health (ASH) campaigns to make quitting smoking easier.

A spokeswoman said the group was generally supportive of the proposals, adding that the therapy is most effective when combined with GP support.

"Nicotine replacement therapy should be more widely available so people can get access to it if they want it," she said.

But ASH would not want to see the therapy provided on the NHS for too long.

She suggested that patients should get the first couple of weeks' treatment free and after that "kick-start" they could pay for their own treatment.

The government is due to publish a White Paper on smoking by Christmas, and the Department of Health declined to comment until then.