Kevin Slater had been in and out of hospital with unexplained symptoms including rapid weight loss and acid reflux for three months by March 1983, when his doctor started to suspect he could be suffering from a new illness called acquired immunodeficiency disorder, or Aids, which had emerged in America two years earlier and was predominantly affecting gay men.

A 20-year-old precision-tool engineer from Cwmbran, in South Wales, Kevin had never been to the United States, he wasn’t gay and he didn’t use intravenous drugs.

If he had Aids, there was only one way he could have contracted it – from Factor VIII, a “miracle” treatment for haemophilia made from human plasma.

Prof Arthur Bloom, Kevin’s doctor at the University Hospital of Wales in Cardiff, was Britain’s leading haematologist. Not wanting to cause panic about Factor VIII, despite his concern that it could be contaminated, Bloom hedged Kevin’s diagnosis and downplayed the risk of Aids for people with haemophilia for months.