A commercial blood product at the centre of the biggest treatment scandal in the history of the NHS was approved for use after government officials were told convicts were among the paid donors and virus contamination “should be assumed”, corporate filings reveal.

The product, given to ­haemophiliacs to enable their blood to clot, was injected into thousands of patients in the UK in the 1970s and 1980s, ­including young children, who were infected with HIV and hepatitis C.

A single batch could contain plasma from 20,000 donors harvested in US prisons and some of the poorest neighbourhoods of America, where drug use and sexual infections were rife. One infected donation would contaminate the entire batch.

An inquiry headed by Sir Brian Langstaff will report next month on the scandal, which has killed about 3,000 people. He has already concluded “wrongs were done at individual, collective and systemic levels”.

The drug firm Bayer provided 7,000 documents to the inquiry, which reveals its subsidiary, Cutter Laboratories, warned in licensing application documents in the 1970s that its commercial blood product Koate, may ­contain viruses. It said: “Since the presence or absence of hepatitis virus in Koate concentrate cannot be proven with absolute ­certainty the presence of such a virus should be assumed.”

The product, known as a factor VIII concentrate, was approved in August 1976 along with similar treatments that were a conduit for deadly viruses for several years.

A government safety committee was told “American state prisons” were among the sources. Studies had shown greater risk of ­hepatitis ­infection from prison-harvested blood and the Committee on Safety of Medicines was warned the product “suffers from being prepared from multi-centre donations which cannot be properly controlled by inspection”.

Des Collins, of Collins Solicitors, acting for 1,500 infected or affected people, said the licensing ­documents were “shocking” and products should not have been approved until viral inactivation was ­available. “There was a huge failure by ­ministers and successive administrations,” he said.

Stuart Cantrill, 50, whose father Barrie died in 1989 from an Aids-related illness after contracting HIV from a commercial blood product for haemophilia, said: “There were clearly some in the NHS and in government who were aware of the risks and chose to ignore them. They went ahead and used a product which was almost ­certain to infect everyone.”

Experts in the 1970s considered the risk of a patient contracting hepatitis B from the pooled products was outweighed by the benefits of treatment, but did not consider the presence of more deadly viruses which had not then been identified, specifically hepatitis C and HIV.

When the cases of Aids were first reported in the 1980s, officials and ministers failed to act over the risk of the disease being spread by the contaminated blood. The Observer flagged the risk in January 1983, warning: “A commercial blood product imported into Britain from the United States may pose a grave threat to the health of haemophiliacs.”

Four months later, the Mail on Sunday warned of “hospitals using killer blood.” It warned the pooled blood products from the US might be infected with HIV and “threatening the lives of thousands of British people”.

It was an accurate and prescient warning, but the government said there was no conclusive proof and failed to withdraw the contaminated product, which then infected adult and child patients with HIV. The infected blood was administered for another two years before heat treatment was ­introduced in 1985. Andy Evans, chair of the Tainted Blood campaign, said it ­“beggared belief” the ­product ­continued to be licensed. “The ­evidence was pointing towards the fact the treatment was dangerous and they failed to act,” he said.

Bayer said it submitted documents voluntarily to the inquiry “to support the inquiry’s understanding of ­historical events and actions of Bayer Group companies”.

It said it was “truly sorry” of the tragic situation that occurred and that therapies designed to save lives caused so much suffering.

• This article was amended on 28 April 2024 because the image used to illustrate the earlier version was not relevant to the subject matter. It was further amended on 1 May 2024: a reference to “dirty blood”, an informal term sometimes used in connection with contaminated blood products, was replaced with “infected blood”; no offence had been intended.