In a prior post, I said it was not clear whether the Speaker of the House of Commons was required to be a member. A couple of scholars have now supplied evidence that strongly suggests that the Speaker was required to be a member.
Andrew Hyman in a comment to my prior post noted the following from a 1708 law dictionary:
Speaker of the Parliament, is an officer in that High Court, who is, as it were, the common mouth of the rest: and as that honorable assembly consists of two houses, so there are two speakers, the one termed the Lord Speaker of the House of Peers, and is most commonly the Lord Chancellor, or Lord Keeper of the Great Seal of England. The other (being a member of the House of Commons), is called the Speaker of the House of Commons; both whose duties you have particularly described in a book entitled, The Order and Usage of Keeping the Parliament.
Also, Seth Barrett Tillman writes with the following evidence:
At the opening of a new Parliament “the lord chancellor confers first with his majesty, and then in his name commands the commons to assemble in their house, and to choose one of their members to be their speaker.”
Henry Elsynge, The Manner of Holding Parliaments in England 155 (London, printed by Richardson and Clark for Tho. Payne 1768) (First print 1660). And:
At the opening of a new Parliament “the Lord Chancellor confers first with his Majesty, and then in his Name, commands the Commons to assemble in their House, and to choose one of their Members to be their Speaker.”
George Petyt, Lex Parliamentaria: or, A Treatise of the Law and Custom of Parliaments 265 (London, Henry Lintot, Third Edition, 1748).