State of Freedom is a social history of the emergence of the modern English state. Given the fact that it's a social history, it's scope is broader than the developments of political institutions, but I found the book to be absolutely fascinating.

I read Frederic Maitland's History of the Common Law for a medieval history class and loved it. It's really well-written and engaging. It covers English common law from the Anglo-Saxon period through to Edward I. Highly recommended.