Originally posted by Marcus Valerius
I think it still qualifies as a constitutional monarchy even if it doesn't have a constitution per se. I believe much of their legal and political system is grounded in tradition and individual laws, rather than an "all-encompassing" constitution as in America. The way I understand it is the term constitutional monarchy simply describes a monarchy that is primarily subject to the rule of law and the parliament rather than the absolute rule of the king. I'm sure one of our British posters can give you an answer in more detail, though....
I can only add that the British constituion evolved rather than was written down. The Office of Priminister only goes back to 1721 when the Hanoverians came to power. The Lord Chancellor (the leader of the Lords) first appeared back to the 13th centuary. I could go with other examples.