More than 50 years after tobacco was shown to cause lung cancer, the most effective measure the NHS has to offer to help people stop smoking is a "brief chat" with their GP, a government watchdog has said.

Five to 10 minutes of one-to-one conversation with all patients who smoke would increase the numbers trying to quit from 33 per cent a year to 50 per cent, the National Institute for Health and Clinical Excellence (Nice) said yesterday. A chat with a doctor or a nurse is also the only cost-effective way of getting people to be more active, Nice said.

Issuing its first public health guidance, Nice said there was a belief among health professionals that trying to persuade people to stop smoking or take more exercise was useless. "Now we can reassure them they are not wasting their breath," said Dagmar Zeuner, the director of public health for Islington Primary Care Trust, north London, and a member of the advisory panel.

She compared the power of a chat with the GP to the discovery of a new drug to stop smoking. "This should be part of the core business of GPs, and smokers have a right to get it."

Stopping smoking is difficult for individual smokers but the benefits to health are so great that even if only two in 100 smokers who receive a six-minute chat go on to give up, the 10 hours of effort by the GP is cost-effective, Nice calculated.