By 2.5mm, you mean 2.5 square mm, right? I looked it up on Wikipedia. That is very close to our AWG 14 - what we use for 15 amp circuits. That would be ~SWG 16. Do you use SWG wire guage or are you metric now?
Mains wiring has been metric pretty well all the time I've been involved in electronics.
Is your electrical code merging with the European sytem? I know ours and the US code are just about completely merged.
No, the UK is completely separate, we wouldn't want to downgrade to a lower standard.
Does this mean you also have a breaker panel with breakers for your individual ring circuits and individual heavy appliances, plus fuses in the ring outlet boxes plus fuses in the toaster or table lamp plugs now? (I was going to say "radio" but they all use wall warts now.)
Each ring main will have it's own fuse in the fusebox, plus each lighting circuit will have it's own fuse as well (like ring mains, usually aseparate circuit for each floor). Then individual heavy appliances (all of which are wired in, not plugged) will have their own direct feeds from the fusebox.
In my house I ran a piece of 6mm cable from the fusebox to the attic, and fitted a separate fusebox on it, powering a single ring main, and a single lighting circuit.
Sockets don't have fuses (apart from the ring main one), but the plug on the end of each appliance does, sized according to the appliance. Maximum size is 13A, giving just over 3000W capability.
If I understand correctly, a "downlighter" is a branch from a ring outlet box that is used to power a ceiling lighting fixture, including a wall switch. Is this correct?
As far as I'm aware a 'downlighter' is just a small light fitting, concealed in the ceiling, and shining directly 'down'. Lights are fed from their own circuits, not from the ring main - and use 1mm cable (or 1.5mm), instead of 2.5mm.