The UK is the world's biggest medical cannabis producer

Charlotte Caldwell claims many youngsters who would benefit from the drug are still not being prescribed it by the NHS. The case of her son Billy, 13, persuaded Home Secretary Sajid Javid to legalise the use of medical cannabis in certain circumstances last year. Cannabis oil hugely reduces the frequency of Billy's life-threatening epileptic seizures.

But Mrs Caldwell claimed he is still unable to get the type of drug he needs on prescription, as doctors say there is