A shadowy Apartheid-era South African paramilitary unit plotted to infect the continent’s black population with Aids, it has been claimed.

An ex-member of the South African Institute of Maritime Research (SAIMR) said the group “spread the virus” at the behest of its eccentric leader Keith Maxwell, who wanted a white majority country where “the excesses of the 1960s, 70s and 80s have no place in the post-Aids world”.

Speaking to the makers of the documentary Cold Case Hammarskjöld, former SAIMR intelligence officer Alexander Jones said Maxwell, who had few, if any medical qualifications, set himself up as a doctor treating poor, black South Africans.

“What easier way to get a guinea pig than [when] you live in an apartheid system?” Jones told the film, which premieres this weekend at the Sundance Film Festival. “Black people have got no rights, they need medical treatment. There’s a white ‘philanthropist’ coming in and saying, ‘You know, I’ll open up these clinics and I’ll treat you.’ And meantime [he is] actually the wolf in sheep’s clothing.”

The documentary makers found a sign advertising the services of a “Doctor Maxwell” in Putfontein, near Johannesburg, and spoke to locals who remembered a man who had a virtual monopoly on the area’s healthcare, despite offering strange treatments.

Anti-Apartheid Movement: in pictures Show all 18 1 /18 Anti-Apartheid Movement: in pictures Anti-Apartheid Movement: in pictures Demonstration in London to launch the Boycott Month of Action, 28 February 1960 Museum of London / Henry Grant Anti-Apartheid Movement: in pictures Demonstration in London in protest against the Sharpeville massacre, 27 March 1960 Museum of London / Henry Grant Anti-Apartheid Movement: in pictures 'No British Arms for South Africa' march and rally, 17 March 1963 Henry Grant Anti-Apartheid Movement: in pictures An area designated for 'white persons only' in Capetown, 1970 A United Nations photograph by Kay Muldoon Anti-Apartheid Movement: in pictures All-night vigil in support of Solomon Mahlangu who was executed by the apartheid government, 1979 Courtesy of the News Line Anti-Apartheid Movement: in pictures Demonstration in Trafalgar Square, 25 March 1990 Courtesy of the International Defence and Aid Fund for Southern Africa Anti-Apartheid Movement: in pictures Poster promoting demonstration in Trafalgar Square, 1990 Anti-Apartheid Movement: in pictures A small selection of the many badges designed and produced by the Anti-Apartheid Movement Anti-Apartheid Movement Anti-Apartheid Movement: in pictures Poster encouraging shoppers to boycott South African goods, produced by the Anti-Apartheid Movement Anti-Apartheid Movement Anti-Apartheid Movement: in pictures Stickers encouraging shoppers to boycott South African goods Anti-Apartheid Movement Anti-Apartheid Movement: in pictures Poster highlighting the discrimination of the apartheid system, 1970s Anti-Apartheid Movement Anti-Apartheid Movement: in pictures Poster produced as part of the 16-year campaign to force Barclays to withdraw from South Africa, 1970s Anti-Apartheid Movement and the National Union of Students FORWARD TO FREEDOM Anti-Apartheid Movement: in pictures Poster produced as part of the consumer boycott campaign, 1980s Anti-Apartheid Movement Anti-Apartheid Movement Anti-Apartheid Movement: in pictures Poster in the classic black-and-white style of the Anti-Apartheid Movement, 1980s Anti-Apartheid Movement Anti-Apartheid Movement: in pictures Poster protesting against the planned 1970 Springboks cricket tour, 1970 Anti-Apartheid Movement Anti-Apartheid Movement: in pictures Poster protesting against the planned 1970 Springboks cricket tour, 1970 Anti-Apartheid Movement Anti-Apartheid Movement: in pictures Poster produced in support of the Sharpeville Six who were sentenced to death after joining a demonstration at which a black deputy mayor was killed, 1988 SATIS (Southern Africa - the Imprisoned Society) Anti-Apartheid Movement: in pictures Poster produced as part of the campaign to end military and nuclear collaboration with South Africa, 1980s World Campaign against Military and Nuclear Collaboration with South Africa

One local shopkeeper said the so-called doctor had given “false injections”.

Mr Jones said SAIMR also operated outside South Africa, telling the documentary: “We were involved in Mozambique, spreading the Aids virus through medical conditions.”

SAIMR is long thought to have had covert ties to Apartheid South Africa’s armed forces.

It has also been accused of working with British intelligence and the American CIA to assassinate UN Secretary General Dag Hammarskjöld.

The Swedish-born secretary general, a supporter of decolonisation, died in mysterious circumstances when his plane exploded just before landing in Zambia in 1961, as he tried to broker a peace between the newly independent Congo and the breakaway province of Katanga.

In 1998, post-Apartheid South Africa’s Truth and Reconciliation Commission revealed it had found letters on SAIMR-headed notepaper which seemed to suggest that British intelligence and the CIA had agreed that “Hammarskjöld should be removed”.

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Both Britain and the US denied involvement in any assassination plot, with the CIA dismissing the suggestion as “absurd and without foundation”.

Maxwell, who died in 2006, was an eccentric who liked to dress up in the style of an 18th Century admiral and give himself the rank of “commodore”.

It is not clear to what extent the alleged late 1980s Aids plot was just one of his fantasies, or whether he had access to the expertise and funding needed to turn it into reality.

An Observer article written with the assistance of the documentary’s co-producer Andreas Rocksen and its director Mads Brügger reveals the filmmakers were able to find writings in which Maxwell seemed to delight in how Aids might decimate the black South African population.

In one of the newly discovered documents, Maxwell wrote: “[South Africa] may well have one man, one vote with a white majority by the year 2000. Religion in its conservative, traditional form will return. Abortion on demand, abuse of drugs, and the other excesses of the 1960s, 70s and 80s will have no place in the post-Aids world.”

Some of Maxwell’s former associates, however, insist his interest in Aids was benevolent rather than genocidal.