Wolfgang, thank you for the link to The Guardian. The people quoted are genuine experts rather than TV punmdits. This is a troubling report that everyone on this thread should read.

If the war was undertaken because of a genuinely perceived threat from Iraq's (presumed) WMD, it may not be illegal under the Charter, which allows nations the right to defend themselves unilaterally; one difficult legality question is whether the Charter
can be interpreted as permitting a pre-emptive defense. The fact that Hussein had defied numerous UN resolutions on WMD over a period of years relates directly to America's decision to go to war and further complicates the "legality" question, as does the fact that the American action was not even unilateral.

Kofi Annan's personal opinion is hardly sufficient to declare a war "illegal". A resolution passed by member nations would be more to the point.

The pressing issue for Americans and Britons is not the war's "legality." It is, as several posters have said, what to do next to avoid a debacle in Iraq.