While reading through Hansard to research a separate question, I came across the following exchange:
Mr Speaker: Order. Someone has flashed a camera. It is quite serious to take photographs in the Chamber. If the Member knew they had taken a photograph, I would expect them to leave the Chamber. It is totally unacceptable to disrupt the Prime Minister when he is speaking.
Ben Bradley: It was an accident.
Mr Speaker: I hope the photograph is deleted. Go out and have a chat with the Serjeant at Arms, because it did not look that way to me.
Paragraph 21.36 of Erskine May indeed confirms that photography is against the rules of the house, but the reference for this statement is a 2013 ruling by the late David Amess, who was chairing a Westminster Hall debate, and a 2018 booklet entitled Rules of behaviour and courtesies in the House of Commons, neither of which seem likely to be the original source of this rule.
What is the origin of this rule, and what was the justification for it? In particular, I wonder whether the justification was related solely to the disruption caused by photography - as the Speaker seems to allude to in this example - or some other concern.