The UK doesn't actually have a written Constitution. Their Constitution is basically precedent. Arguably the entire government is more of a norms/customs thing and has evolved through English History.

If you have an audible account, I can recommend the various Great Courses on English History. An interesting sub theme of all of them is the evolution of the English government based on evolving norms and customs. I'm not aware of any good source that focuses on the topic, but I'm sure something exists, and now I might ask for one on Book Club Wednesday.