The scientist who first linked smoking to lung cancer was paid by a chemicals firm while investigating cancer risks in the industry, it has emerged.
Sir Richard was an acclaimed scientist
Professor Sir Richard Doll held a consultancy post with US firm Monsanto for more than 20 years.
During that time he investigated the potential cancer causing properties of the powerful herbicide Agent Orange, made by the company.
But a former colleague said he gave money he was paid to charity.
Professor Sir Richard Peto, a fellow expert in cancer, said there were no rules governing disclosure of consultancies of this type 20 years ago.
He said: "Everybody working in this area knew that Richard worked for industry and consulted for industry, and would do court cases.
"It does not in any sense suggest that his work was biased. He was incredibly careful to avoid bias."
The BBC has seen private letters which show that Sir Richard, who died in 2005 aged 92, received a US$1,500-a-day consultancy fee from Monsanto in the mid-1980s.
During that period, Sir Richard wrote to an Australian commission on the results of his investigation into whether Agent Orange, famous for its use by the US during the Vietnam War, caused cancer.
He argued in his letter that there was no evidence that Agent Orange caused cancer.
Should come clean
Professor Lennart Hardell, of the Oncology Department at University Hospital Orebro, Sweden, has also studied the potential hazards posed by Agent Orange.
He was one of the scientists whose work was dismissed by Sir Richard.
He told the BBC Sir Richard's work was tainted.
He said: "It's quite OK to have contacts with industry, but you should be fair and say 'well, I'm writing this letter as a consultant for Monsanto."
"But he does it as president, Green College, UK - a prestige position; also the Imperial Research Cancer Organisation in the UK.
"And that makes a different position of the paper because you are an official university-employed person giving this position."
Further documents obtained by The Guardian newspaper allegedly show that Sir Richard was also paid a £15,000 fee by the Chemical Manufacturers Association, and chemicals companies Dow Chemicals and ICI for a review of vinyl chloride, used in plastics, which largely cleared the chemical of any link with cancers apart from liver cancer.
According to the newspaper, this is a view with which the World Health Organisation disagrees.
Sir Richard's views on the chemical were used by the manufacturers' trade association to defend it for more than a decade, The Guardian said.
Sir Richard was the first to publish a peer-reviewed study, in 1951, to demonstrate smoking was a major cause of lung cancer.