Secret documents reveal that government-funded experts were warned nearly 30 years ago that tranquillisers that were later prescribed to millions of people could cause brain damage.However, no such work was ever carried out into the effects of drugs such as Valium, Mogadon and Librium – and doctors went on prescribing them to patients for anxiety, stress, insomnia and muscle spasms.

MPs and lawyers described the documents as a scandal, and predicted they could lead the way to a class action costing millions. There are an estimated 1.5 million “involuntary addicts” in the UK, and scores display symptoms consistent with brain damage.