Which term describes established practices that are not legally enforceable within the UK constitution?

The term that accurately describes established practices that are not legally enforceable within the UK constitution is conventions. Conventions are unwritten rules that govern the behavior of various political actors and institutions, setting out how certain situations should be handled based on tradition and longstanding practice rather than formal legal statutes.

For instance, the Prime Minister is expected to be a member of the House of Commons, not the House of Lords, which is a convention that shapes the functioning of the UK government even though there is no law mandating it. These conventions play a crucial role in the political culture and operational practices of the UK, ensuring a degree of stability and predictability in governance without the rigidity of legal enforcement.

In contrast, statutes are laws enacted by Parliament and are legally enforceable, regulations refer to rules made under statutes to provide guidelines for implementation, and declarations usually pertain to formal statements or announcements rather than established practices. This distinction highlights why conventions are particularly significant in the context of the UK's uncodified constitution.