Hi Edward,
Start here: https://register-drones.caa.co.uk/drone-code/getting-what-you-need-to-fly (bearing in mind the class marks are not in force yet (see later))
And then check out: Where can I fly my drone in the UK? - Good 2 Go - Can I fly my drone here?
In summary, your Nazgul is treated like any other drone, so its weight, where, how close to other people you are intending to fly, and any authorizations you may hold all come into play when determining the legality of your intended flight. Plus, you need a spotter while you’re flying FPV.
The new rules that were going to be introduced in the new year are now on hold. Catch up with what’s going on there in this thread: