Our cousins across The Pond do have a constitution. The problem is that it is not a single document like ours. (New Zealand is in the same position, being a member of the commonwealth and all.) So you can't simply go to a book and look up a particular provision. Rather, their constitution consists of a collection of rights, principles, legal cases and the like which make figuring out what is and is not "constitutional" in the land of warm beer a real muddle.