Four of the black workers have died and a number of the others are suffering severe brain and other neurological damage.
The workers had accused Thor Chemicals Holdings, of Margate, in Kent, of adopting working practices in South Africa which would not have been allowed in Britain.
Yesterday's landmark settlement, which followed the filing of claims for damages in the High Court in London, has serious implications for British businesses with operations in developing countries.
The settlement was announ-ced after a report in The Independent last month highlighted the case. Similar claims are being pursued against other Brit-ish companies owning uranium mines and asbestos plants in southern Africa.
One of the Thor workers, Albert Dlamini, 30, received pounds 100,000 for injuries which have left him walking on crutches and unable to speak properly. He said: "Working for Thor has destroyed my life. I feel very bitter that this British company has come to my country and adopted working practices that would never have been accepted in its own country."
The workers first realised something was seriously wrong when three men were taken into hospital in 1992, suffering from severe mercury poisoning.
Peter Cele, 21, died seven months later. Englebert Ngcobo, 55, was in hospital for three years before he slipped into a coma and died.
They had all worked at Thor's mercury plant at Cato Ridge in Natal. The operation had been set up by the English parent company using technology and systems of operation which had been developed in Britain.
Thor had operated a mercury plant at Margate which, during the 1980s, was repeatedly criticised by the Health and Safety Executive for bad working practices and the over-exposure of British workers to mercury.
Under pressure from the HSE, Thor closed down its mercury operations in Britain in 1987 and expanded them in South Africa, where the plant relied on Zulu-speaking casual, untrained and unskilled labour.
In bringing their claim, which was also made against the Thor chairman Desmond Cowley, the workers enlisted the support of experts in occupational medicine and toxicology.
In their evidence, the workers testified that rather than trying to reduce mercury levels in the environment, the company adopted a policy of trying to control mercury exposure by replacing workers who had high levels of mercury with new casual employees. Others, they said, were sent to work in the garden until their mercury levels dropped.
Thor had fought to prevent the workers' claims being heard in a British court, even appealing to the House of Lords. But the case had been set for a three-month trial in October.
No one at Thor was available for comment yesterday.