Only MI5/GCHQ/OSCT can answer your questions with actual numbers.
(EDIT)
There are several studies on effectiveness of camera surveillance on crime prevention.The UK unlike other nations actually has a lot of material here.
I haven't followed up. Are these numbers published? If not, I would tend to assume that they are too embarrassing to show. But despite my bias, I'm actually curious.
https://www.tandfonline.com/doi/full/10.1080/10242694.2011.6...