I don't think this is true. Apparently the operation of a large majority of those private cameras is in fact outsourced to a handful of big security companies, and many of them are remotely operated. This makes getting access to private cameras a lot easier for police than you think.
If you've ever had to deal with the UK police as a victim of a crime, you'll quickly find out they're pretty useless at obtaining CCTV footage. I was asked to get it myself, to which the business who owned the CCTV told me they would only hand it to the police, so nothing happened.
