England's chief medical officer has raised fears that vaping is “a ticking time bomb” which could do long-term harm, amid growing concern about the safety of e-cigarettes.

Prof Dame Sally Davies, who will stand down later this month, made the comments just before Donald Trump announced plans to ban flavoured vaping products, in a bid to discourage children from taking up the habit.

In an interview with Civil Service World, Dame Sally raised concerns about the evidence to support the safety of e-cigarettes.

“Is this a ticking time bomb? Will they turn out to have long-term consequences?” she said.

Public Health England has thrown its weight behind vaping, stating it is at least 95 per cent less harmful than smoking. Last year it urged hospitals to start selling e-cigarettes and letting patients vape indoors – and even in bed.

Official statistics suggest that when it comes to teenage experimentation, vaping has replaced smoking.

The NHS figures show 25 per cent of children aged 11 to 15 have tried e-cigarettes, while 16 per cent have had conventional cigarettes – down from a high of 49 per cent in the Nineties.