In the early 1980s, the UK could not keep up with demand for Factor VIII, which was made by pooling – or mixing – the blood plasma of thousands of individual donors.

Instead the treatment was shipped from the US.

In the UK, blood donations have always been voluntary, but in the US, drug companies were allowed to pay cash for plasma.

High risk groups, from prisoners to drug users, had a clear financial incentive to give blood and potentially lie about their medical history.

Evidence uncovered by campaigners and seen by the ongoing public inquiry into the wider contaminated blood scandal shows that, as the risk from Aids started to become known, a series of clear warnings were sent to the UK government.

In May 1983, Dr Spence Galbraith, the director of the UK’s Communicable Disease Surveillance Centre, wrote to Dr Ian Field, the senior principal medical officer at the Department of Health, urging that all US blood products should be withdrawn from use until the risk of Aids was “clarified”.

The letter from the British embassy in Washington – which Panorama has now seen – was also sent to Dr Field, just a month later on 28 June 1983.

In it, an embassy official describes a meeting with a representative from the US Centers for Disease Control’s Aids taskforce.

The transmission of HIV in blood was discussed, he writes. Haemophiliacs were “most at risk” from the “dubious habits” of some paid American blood donors, and the mixing of thousands of those donations to make Factor VIII.

The Tainted Blood group, which represents hundreds of survivors and their families, says the letter shows a “staggering level of awareness and detail” about the dangers.

But this – and other – warnings were not acted on. NHS patients continued to be given untreated Factor VIII imported from the US until at least 1985.

Many of those involved in decisions in the 1980s are no longer alive, including Dr Ian Field.

In 1983, knowledge of HIV and Aids was still emerging.

At the time, a Department of Health official described the call to withdraw American Factor VIII as premature and said it did not take into account the risks to haemophiliacs of removing a major source of their treatment.