This article investigates the Crown within the British constitution and gauges its influence upon the decision to deploy troops in Iraq. It considers the functioning of parliamentary checks upon the Prime Ministerial war prerogative in the Iraq decision, specifically the parliamentary debate and vote on March 18, 2003. It identifies how the premiership's colonisation of the Crown enabled Mr Blair to obtain parliamentary approval for warfare despite extensive opposition to the deployment. The appearance of strengthening parliamentary involvement in warfare decisions was largely undercut by, amongst other factors, a cluster of prime ministerial Crown-based prerogatives. Ultimately, the Iraq affair demonstrates that the Crown is not a quaint constitutional abstraction but has real influence on issues of the utmost importance. The notion of monarch remains a subtle but powerful influence in the British prime ministerial war power legally, structurally and culturally, and parliamentary checks in this context may be thus institutionally limited.