With their sleek design and clever marketing, they have been described as the iPhone of e-cigarettes.

But despite being blamed for an epidemic of teenage tobacco addiction in the US, Juul e-cigarettes are being openly promoted to families in British supermarkets, a Mail on Sunday investigation can reveal. Dr Jonathan Winickoff, a professor at Harvard Medical School, has said: ‘If you were to design your ideal nicotine delivery service to addict large numbers of American kids, you’d invent Juul. It’s absolutely unconscionable. [...]