Getting all smokers to switch to electronic cigarettes would be the "greatest health advance since vaccinations," Professor David Nutt claims.

The former government drugs advisor said any side effects of using e-cigarettes would not be as harmful as smoking tobacco.

He told BBC Radio 5 live's Shelagh Fogarty: "I'm totally in favour of this kind of harm reduction approach."

"These electronic cigarettes should not be controlled as medicines - they should be controlled more lightly than cigarettes in order to encourage people to switch."