Vapers could be at risk of developing the deadly disease ‘popcorn lung’ after scientists found a toxic chemical in 75 per cent of flavoured electronic cigarettes.

Diacetyl, a chemical which is used as a butter substitute in flavours like Cotton Candy and Cupcake, has been linked to respiratory disease bronchiolitis obliterans

Although it is thought to be safe when eaten, the United States National Institute for Occupational Safety and Health has said it could be hazardous when inhaled over a long period.