Leading British scientists have come to the defence of Sir Richard Doll, following claims that the Oxford cancer researcher failed to disclose payments from a chemical company.

Sir Richard, who died last year, helped save millions of lives through his groundbreaking work, which established that smoking caused lung cancer.

But an assault has been launched upon his reputation, centring on allegations that he was paid a consultancy fee of $1,500 a day in the mid-1980s by US firm Monsanto.

According to a report in The Guardian, Sir Richard wrote to a commission investigating potential cancer-causing properties of Agent Orange to say there was no evidence that the Monsanto-made chemical caused cancer.

Agent Orange was used as a defoliant by the US forces during the Vietnam War to try to deprive Vietcong guerillas of cover in jungles.

The newspaper said documents showed that Sir Richard received a £15,000 fee from the chemical firms for a review that largely cleared vinyl chloride, used in plastics, of any link with cancers, apart from liver cancer.

A group of eminent scientists led by Prof Colin Blakemore, chief executive of the Medical Research Council and Waynflete Professor of Physiology at Oxford University, said the allegations were being made against "one of the world's greatest cancer researchers", who was not alive to rebut them.

Prof Sir Richard Peto, the Oxford-based epidemiologist, said that it had been widely known that Richard Doll worked for industry.

He added: "It does not in any sense suggest that his work was biased. He was incredibly careful to avoid bias."

Sir Richard, who spent much of his career working with Richard Doll, added that 20 years ago stringent rules governing disclosure of consultancies did not exist.

The attack on Sir Richard was led by Prof Lennart Hardell, who studied the potential hazards posed by Agent Orange, but whose work was dismissed by Sir Richard.

He said: "It is 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 of Green College, a prestigious position, also the Imperial Cancer Research organ- isation in the UK."