BANNING people from smoking e-cigarettes in hospital grounds sends a mixed message about their dangers, a public health expert has warned.

Smoking tobacco products was banned in all Scottish hospital grounds in 2015, but individual health boards can choose whether to allow "vaping" - smoking electronic cigarettes which give smokers a nicotine fix without tobacco.

NHS Fife and Lanarkshire have banned vaping, but NHS Tayside is now set to follow NHS Greater Glasgow and Clyde and NHS Lothian by lifting the prohibition.

Professor Linda Bauld, of Stirling University, said there was little evidence to support a ban and warned that it could discourage smokers from quitting cigarettes.

Writing in an article for the journal, Tobacco Control, Prof Bauld said: "By treating e-cigarettes like tobacco, and banning them in certain places, it gives a message to the public about them being as dangerous as smoking.

"When people made some of these early policies, it was a bit of wild west out there. We need to be shaping these choices based on new evidence."

The Royal College of Physicians previously said the risks from vaping were less than five per cent of those linked to traditional cigarettes.

However, public health experts from Sydney University, Australia writing in an accompanying editorial in the Tobacco Control journal warn that claims vaping emissions are benign are based on "gossamer-thin evidence".

Vaping has also been banned on ScotRail trains since 2013 and is banned in most restaurants and workplaces. However, the new law forbidding smoking in cars with children does not apply to e-cigarettes.

A spokesman for the Scottish Government said: "We are aware that the use of e-cigarettes can help smokers to quit, but they are not risk-free.

"That is why the Scottish Government has legislated to regulate the sale and promotion of these consumer products through the Health Act 2016.

"We will continue to monitor emerging evidence on e-cigarettes."