The most recent edition of Erskine May is available online and is free to use:
Erskine May’s treatise on the law, privileges, proceedings and usage of Parliament is often referred to as ‘the Bible of parliamentary procedure’. It’s the most authoritative and influential work on parliamentary procedure and constitutional conventions affecting Parliament. Rather than a set of rules, Erskine May is a description of how procedure in the House of Commons and House of Lords has evolved and the conventions that apply.
Erskine May is divided into parts as follows: Constitution and Organisation of Parliament; Powers and Privileges of Parliament; Conduct of Business; Public Legislation; Financial Procedure; Committees; Private Legislation.
The Speaker regularly cites Erskine May in his rulings and it is often referred to during debate in the Commons. It’s also relied on by people with a professional interest in Parliament and parliamentary practice.