In late 1985, Norman Fowler, who was then the health secretary in Margaret Thatcher’s government, sent a letter to the prime minister. He said that there had been 275 people with Aids in the UK that year. Of these, 144 had died. Without action, he added, a further 20,000 people would be infected with HIV by 1988. The UK was on the precipice of a public health emergency. Fowler encountered a lot of scepticism.