One in three medics would not recommend e-cigarettes to smokers, with quarter unsure if they are any safer than smoking, polling suggests.

The survey of more than 500 cancer specialists, GPs and nurses found more than half said they did not know enough about vaping to make recommendations to their patients.

It comes despite advice from Public Health England (PHE) which suggests the devices are at least 95 per cent less harmful than cigarettes.

Researchers asked medics if they would recommend e-cigarettes to cancer patients who had continued to smoke after their diagnosis.

Smoking increases the risk of treatment complications, disease recurrence, and the development of further tumours, increasing the risk of death.

The study found that 29 per cent of health professionals said they would not recommend patients switched to e-cigarettes, while 25 per cent did not know if they were safer than smoking.

Researchers said that health workers need more training, to help them advise patients better.

The new survey, presented to the 2018 National Cancer Research Institute Conference in Glasgow, found most of those polled either did not know if their hospital had any guidance on the matter, or thought they did not.

Lead researcher Dr Jo Brett, from Oxford Brookes University,said: "Smoking is a well-established risk factor for many common cancers. It is the single biggest avoidable cause of cancer in the world.