The Clerk of the Commons isn't a member of the House, and therefore has no standing in debates or other transactions. They were, however, responsible for administering the appointment of the Speaker at the beginning of each Parliament and whenever a Speaker left the role mid-parliament. Usually, a Speaker is chosen by consensus, and is unopposed on the day, being appointed simply by a motion. Therefore, it was a duty the Clerk could execute even without being able to address MPs directly. They would point to an MP who would propose the motion, and that was that.
The 1971 Speaker election was controversial because, while one of the main roles of the Speaker is traditionally to ensure the backbenchers are heard and can hold ministers accountable, unusually the sole candidate - agreed upon by the frontbenches of the Tories and Labour in advance - was a former minister himself. In fact, Selwyn Lloyd had been Minister of Supply under Churchill, Minister of Defence under Eden, Foreign Secretary under Eden and Macmillan, Chancellor of the Exchequer under Macmillan and Leader of the Commons under Douglas-Home. There was a disquiet among the backbenchers that Lloyd may have too much interest in the Government's rights rather than those of backbenchers. Lloyd had been chosen by negotiation by the leadership of both main parties, and this too added to the sense that backbencher dissent, long a hallmark of the House of Commons, may have been in danger of being reined in.
On the day, a crossbench rebellion nominated Sir Geoffrey de Freitas, a backbench MP and former High Commissioner to Ghana, to stand against Lloyd. This was not sought by Sir Geoffrey, who urged people not to vote for him. The New York Times reported:
Mr. Lloyd had been agreed upon by the leaders of the Conservative and Labor parties and had been expected to be elected routinely without opposition. But annoyed backbenchers of all parties rose to complain that they had not been consulted.
In a gesture of defiance, a Conservative backbencher, Robert Maxwell‐Hyslop, nominated a surprised Labor member, Sir Geoffrey de Freitas, for the post and demanded a recorded vote It was only the second contest for the Speaker's chair in more than 70 years.
The Clerk, not being able to address an MP directly, was powerless to bring order to what was suddenly a contentious debate. Though it went unusually to a division, Lloyd was elected speaker. Immediately Harold Wilson, Leader of the Opposition, expressed his opinion that the procedure for appointing a Speaker should be changed in future:
We should seek to provide a degree of consultation, the lack of which has led to perhaps some unfortunate and unhappy events this afternoon; but perhaps should also look for a procedure to enable the House when electing a Speaker in future, if this is to follow a Speaker's retirement, to do so in a more orderly and seemly manner.
In 1972, House of Commons Standing Order 1 - that which governs the election of the Speaker - was amended. The powerless Clerk was removed of his duty in the matter, and in their place
the chair shall be taken by that Member, present in the House and not being a Minister of the Crown, who has served for the longest period continuously as a Member of this House.
This ensures that the chair is held by a backbencher, and is intended to maintain the Speaker's distance from the frontbench. Moreover, the chair is temporarily given all the Speakers' powers, thus can keep the proceedings orderly. In a situation, like in 1971, where the outgoing Speaker has resigned mid-Parliament, the 1972 alterations now kept them in situ until the election is concluded.
Other changes included a secret ballot rather than a Division, and that candidates must be nominated in writing the morning of the election. One of the conditions of the nomination is the nominee's signature of consent, so no-one can again be ambushed like poor Sir Geoffrey.