I've read that London has a lot of surveillance cameras, but most are privately owned, not directly controlled by the government nor the police. Is it true? Who control them? How it works?
Anecdote: A manager of a Fortune 50 location I was working at received a call from HQ to keep an eye on a known perp who entered the store no more than 5 minutes prior to the call. Very impressive & very scary.
Human memory is both unreliable anyway and motivated in operation. CCTV acts as an impartial witness. It doesn't automatically have all the facts, but it is reliable and unmotivated. Knowing this impartial witness has their backs enables your employees to obey policy without worrying about how that will be remembered.
The operators are supposed to do some paperwork establishing they've thought about how they're going to treat all this data, and if they want to put CCTV somewhere you'd normally expect to be private (e.g. a changing room or toilet) they need to tell the cops what they're doing and why (e.g. to investigate a specific employee suspected of theft) before they do it otherwise that's a crime.