LONDON (Reuters) - More than one million Iraqis have died as a result of the conflict in their country since the U.S.-led invasion in 2003, according to research conducted by one of Britain’s leading polling groups.

Mourners carry a flag-draped coffin of a shooting victim during a funeral in Amil district in Baghdad January 21, 2008. More than one million Iraqis have died as a result of the conflict in their country since the U.S.-led invasion in 2003, according to research conducted by one of Britain's leading polling groups. REUTERS/Ahmed Malik

The survey, conducted by Opinion Research Business (ORB) with 2,414 adults in face-to-face interviews, found that 20 percent of people had had at least one death in their household as a result of the conflict, rather than natural causes.

The last complete census in Iraq conducted in 1997 found 4.05 million households in the country, a figure ORB used to calculate that approximately 1.03 million people had died as a result of the war, the researchers found.

The margin of error in the survey, conducted in August and September 2007, was 1.7 percent, giving a range of deaths of 946,258 to 1.12 million.

ORB originally found that 1.2 million people had died, but decided to go back and conduct more research in rural areas to make the survey as comprehensive as possible and then came up with the revised figure.

The research covered 15 of Iraq’s 18 provinces. Those that not covered included two of Iraq’s more volatile regions -- Kerbala and Anbar -- and the northern province of Arbil, where local authorities refused them a permit to work.

Estimates of deaths in Iraq have been highly controversial in the past.

Medical journal The Lancet published a peer-reviewed report in 2004 stating that there had been 100,000 more deaths than would normally be expected since the March 2003 invasion, kicking off a storm of protest.

The widely watched Web site Iraq Body Count currently estimates that between 80,699 and 88,126 people have died in the conflict, although its methodology and figures have also been questioned by U.S. authorities and others.

ORB, a non-government-funded group founded in 1994, conducts research for the private, public and voluntary sectors.

The director of the group, Allan Hyde, said it had no objective other than to record as accurately as possible the number of deaths among the Iraqi population as a result of the invasion and ensuing conflict.