A more thorough explanation:

LEX ET CONSUETUDO PARLIAMENTI

Lex et consuetudo parliamenti is a Latin term that refers to the law and custom (or usage) of Parliament in history.

• One example of lex et consuetudo parliamenti is the tradition of the Speaker of the House of Commons wearing a wig and gown during parliamentary sessions.
• Another example is the practice of the Prime Minister answering questions from Members of Parliament during Question Time.

These examples illustrate how lex et consuetudo parliamenti refers to the established laws and customs that govern the proceedings of Parliament. These traditions have been passed down over time and are considered an important part of parliamentary procedure.