The programme, entitled 'Britain's most dangerous drug', will be broadcast at 9 pm.

The pair will talk about the current classification of drugs and a recent paper suggesting that it is not based on sound scientific basis. They will also explain how it can hinder research and treatment – for instance, how they think that the Class A drugs LSD and ecstasy could be used to cure people with chronic mental illnesses.

The Psychopharmacology Unit, in the Department of Community-Based Medicine, is well known for its groundbreaking work on brain function, addiction and drugs.

Programmes in the Horizon series are archived on the BBC website after they have been broadcast.