Thanks, all
That concurs with what I remember from a seminar by James Eade at a PLASA just after the 18th Edition came out (or was due out) - i.e. Type A C Curves. And the video was very useful!
My doubts were raised by a retired electrician who not only said that RCBO/RCDs weren't needed, but that B Curves would do (old dogs and new tricks come to mind!).
Thankfully, that was elsewhere and he is not involved in this install. I can now price up the parts and get a spark booked.
Yes, I had intended to have 20amp DP switches installed for isolation, but I'm not sure whether to have these with neon indicators because I know they can make some domestic LED fittings glow. I don't know if this would be an issue. I would prefer them as an easy visual check that everything is off.
I'm planning on about 10 fixtures per circuit. But, having watched that video, I might suggest installing a separate distro just for the LEDs, with multiple circuits. I'll have to see how it goes.
Thanks again!