A short guide to the constitutional framework of the United Kingdom
The United Kingdom does not have a constitution
The UK has no written constitution. Nor does England have a constitution, neither written nor formulated. The United Kingdom is one of the few countries of the world that does not have a written constitution: it just has what is known as an "uncodified constitution".
Thus the only "British Constitution" that exists is a set of rules and regulations constituted by jurisprudence and laws (English and Scottish law), and by various treaties and international agreements to which the United Kingdom has signed up. This uncodified constitution has largely developed out of historic English law, since many of its founding principles and essential laws go back to charters and bills that were drawn up by the English parliament long before the creation of the United Kingdom.
https://about-britain.com/institutions/constitution.htm