"The science around the safety of E-cigarettes has not been demonstrated," the World Health Organisation's Glenn Thomas told ITV's Tonight.
"We still need more research to know and understand what sort of impact on health.. these E-cigarettes are having."
"We know that a lot of the toxins which are consumed through E-cigarettes have not been adequately researched," he added.
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Rain will clear eastwards through Sunday but it will remain blustery.