I cannot think of any circumstances in which a government can go to war without the support of parliament.

In April 1991, after the Gulf war, Iraq was given 15 days to provide a full and final declaration of all its WMD.

The threat today is not that of the 1930s. It's not big powers going to war with each other. The ravages which fundamentalist political ideology inflicted on the 20th century are memories. The Cold war is over. Europe is at peace, if not always diplomatically.