If you want a little light reading then CAP722 on the CAA website is probably what you are looking for and will lead you to other documents. Then go and look up the BNUC-S qualification... then go and look at the price!!:dejection:
Although, I was speaking to someone the other day who said that a lot of the documents on the CAA site are already out of date and changes are happening. As someone who would like to offer a service as "another small string to my bow"

, I have done a fair amount of research but a lot of the information seems to be conflicting, outdated or just wrong. Things really start to change when you are doing "aerial work" rather than just, for example, catching some nice sunsets for a Youtube montage.
The interesting thing about BNUC-S from what I have been told is that it will be graded and each platform you use will require a different test. So if you had a hex carrying one FC but then decided to have an octo with WKM for heavier lifting you would have to have another test done. I'm not sure if that would be at full price again or a smaller fee. There is also the option of having an airworthiness certificate for each machine. Effectively each individual craft you use will have its own registration number that will be used when seeking permission from the CAA. There seems to be a bit of a monopoly at the moment and I think more training providers would be needed to drive prices down. At the moment, it is alot of upfront cost for not a huge return!