Before the donation from the Saab-British Aerospace consortium in July, the trade union had been opposed to the deal to supply BAe Hawk and Saab Gripen fighter aircraft to the South African air force.
Politicians in Britain, Sweden and South Africa believe the pounds 3bn deal and other "economic sweeteners" attached to it raise serious ethical questions.
The money will go towards establishing an "Industrial School" for the National Union of Metalworkers of South Africa (Numsa) and is being channelled through two Swedish trade unions, Metall and the Union for Clerical and Technical Employees in Industry.
Although the British police have found nothing illegal, Ann Clwyd, Labour MP for Cynon Valley and a prominent member of the Commons Select Committee on Strategic Arms Exports, said last night she would put the issue of these sweetener deals called "offsets" on the committee's agenda.
Pressure is also growing in Sweden, where Saab is based, for the deal to be investigated by a joint Swedish-South African parliamentary commission. Patricia de Lille, an MP for the left-wing Pan Africanist Congress, has accused members of the ANC government in parliament of taking kickbacks, enjoying foreign holidays and setting up companies to benefit from the deal.
None of the allegations of corruption has been substantiated but the Heath Commission, set up by Nelson Mandela to investigate allegations of state corruption, is considering making preliminary inquiries into the deal, according to the commission's spokesman.
The deal between the union and Saab-British Aerospace was signed in July - nine months after the South African government announced Saab-British Aerospace was the preferred bidder with its offer of 28 JAS39 Gripen fighter aircraft and 24 BAe Hawk 100 trainer aircraft.
BAe, which has a 35 per cent stake in Saab, was later told the order was to be cut to nine Gripens and 12 Hawks, after pressure to put more money into poverty relief and education.
As part of the deal BAe agreed an "offset" package of investments to re-equip South African defence industry factories so they could supply parts for the Hawks and Gripens.
Peter Hain, the Foreign Office minister with responsibility for Africa, yesterday told The Independent on Sunday that the Government would investigate the deal if any substantiated allegations were made.
He has praised the deal as a model of ethical trading and claimed that "nobody could object to Britain selling arms to South Africa". However, it appears that many South Africans object to the deal and are beginning to question exactly who will benefit most from the lucrative "offset" deals.
A spokeswoman for the Metropolitan Police confirmed that detectives had made preliminary inquiries into an allegation of corruption. She added: "The case is not closed and would be reactivated if further evidence was brought to our attention."Reuse content