There is no such thing as a "precedent law". Commonlaw is made up of precedents, going all the way back to the foundation of the Kingdom of England. Everytime a law is made in Parliament, and someone has fallen afowl of that law, and there are special circumstances then the Judge can set a precedent in common law.
Parliament basically says we create the laws, and you the Judicary interpret our law, therefore creating precedents. It's always been like that.