If it’s just for CCTV, then look at using POE (power over ethernet) which will allow you to run just a single cable to each camera as it will do data and power. You will probably need a switch or router that provides POE, assuming your current one doesn’t (extremely unlikely if it’s a residential one, particularly from BT). Just check the distance you need to cover for compatibility.
I like Ubiquiti’s stuff, and they have specific setups for POE switches, cameras, and recorders for CCTV and are pretty well regarded. You can continue to use your BT hub, just plug it in to the Ubiquiti setup, no issues with capacity or anything else. If you can’t run a cable, they also have long range wireless bridges that might work for you, although you will need power at both ends (not needing power is why POE is so compelling if you can make it work).
Don’t forget the polishing cloth!