Kevin,

"In the run up to the war the argument was frequently presented that in these circumstances the burden of proof that he did not have WMDs should lie on Saddam's regime."

Please correct me if I am wrong, but having accepted the terms of UN Security Council Resolution 1441, Saddam Hussein's regime were required to make a full and accurate declaration on their WMD stocks, weapons and weapons programmes (7th December, 2002). That declaration was considered to be inadequate by the heads of the UN inspection teams as it cast no further light on what had happened to outstanding WMD stocks and weapons that were known to exist in 1998 (UNSCOM report January 1999)

Now as far as is known that still remains to be the case, and will continue to be the case, even if no WMD's are found in the aftermath of this war, once Saddam Hussein has been removed from power.

So your contention that:

"...in the wake of a war in which they had not been used, the burden of proof would surely have to lie on those who claimed that he did have those weapons, but had failed to use them."

Is absolutely ridiculous, because according to information held, and accepted, by the United Nations, there are clear points of difference between the UNSCOM report and the latest Iraqi declaration. All anybody wanted to know was what happened to the outstanding items detailed, between December 1998 and March 2003. People within the Iraqi government, civil service and military were the only people who could fully answer the issues and questions posed by the UN weapons inspectors and they were afforded every chance to do so - they didn't.

There is no question at all about there being any burden of proof on the part of the US or UK governments to prove that those weapons are there - The entire Security Council of the United Nations in January 1999 knew they were there - What that same international body want to know now is where are they now? What has happened to them?