Britain must hold an inquiry into the invasion of Iraq as the fifth anniversary of the war approaches, according to a Birmingham peer.
Lord Fowler, the former MP for Sutton Coldfield, said Britain must learn from its mistakes, as he led a debate in the House of Lords.
He was backed by colleagues including former Foreign Secretary Lord Owen, but ministers said no inquiry should take place until the conflict was over.
The invasion of Iraq by the United States and its allies including the UK began on March 20, 2003.
Lord Fowler said: "In a few weeks' time, in March, we will come to the fifth anniversary of the start of the conflict in Iraq. I want to renew that call for an inquiry because I know of no other way that the lessons from this conflict can be learned."
He said he had backed the invasion during the heated arguments in the run-up to the war but now believed he had been misled by Tony Blair.
An inquiry was important because under-standing the causes of the war would mean understanding why so many people had died, said Lord Fowler.
"First and foremost, there have been the casualties of this conflict - the British troops who have been killed and injured.
"Regiments such as the Royal Anglians, of which my old regiment is now part, have suffered badly. But of course the chief casualties have been among the Iraqis themselves. Some have died in the fighting, some have died in the sectarian murders that have accompanied the fighting, and some have died in the criminality which we have been unable to control.
"No one knows exactly how many have died. A conservative estimate is 100,000, but there may well be many thousands more; I doubt that there have been fewer."
The conflict had also created millions of refugees, he said.
"Finally, the public are certainly entitled to ask whether our troops have always been properly equipped and supported for the conflict".
The comments were backed by Lord Owen, a former Labour Foreign Secretary and founder of the SDP, who referred to his career as a doctor before becoming a politician.
He said: "In my profession, there is a tradition that, when you make a mistake, you have a post mortem."
He had supported the war five years ago, he said. "I have made mistakes. Many of us have made mistakes. We should face up to them."
Foreign Minister Lord Malloch-Brown said there was likely to be an inquiry, but not now.
"The position of this Government is that indeed a time may come - and I suspect definitively will come - when such an inquiry is necessary. But we would still maintain that we have not yet reached it now." ..SUPL: