A study that claimed 650,000 people were killed as a result of the invasion of Iraq was partly funded by the antiwar billionaire George Soros.

Soros, 77, provided almost half the nearly $100,000 cost of the research, which appeared in The Lancet, the medical journal. Its claim was 10 times higher than consensus estimates of the number of war dead.

The study, published in 2006, was hailed by antiwar campaigners as evidence of the scale of the disaster caused by the invasion, but Downing Street and President George Bush challenged its methodology.

New research published by The New England Journal of Medicine estimates that 151,000 people - less than a quarter of The Lancet estimate - have died since the invasion in 2003.

“The authors should have disclosed the [Soros] donation and for many people that would have been a disqualifying factor in terms of publishing the research,” said Michael Spagat, economics professor at Royal Holloway, University of London.

The Lancet study was commissioned by the Massachusetts Institute of Technology (MIT) and led by Les Roberts, an associate professor and epidemiologist at Columbia University. He reportedly opposed the war from the outset.

His team surveyed 1,849 homes at 47 sites across Iraq, asking people about births, deaths and migration in their households.

Professor John Tirman of MIT said this weekend that $46,000 of the approximate $100,000 cost of the study had come from Soros’s Open Society Institute.

Roberts said this weekend: “In retrospect, it was probably unwise to have taken money that could have looked like it would result in a political slant. I am adamant this could not have affected the outcome of the research.”

The Lancet did not break any rules by failing to disclose Soros’s sponsorship.