Black Knight is right - I have seen MCBs trip on a few occasions and lo and behold on Saturday exactly the same thing happened when I turned on the landing light to start pulling the cables!

As stated earlier, there's a right way and a wrong way to do this. My advice would be to put the extra work in and those floor boards lifted.

If it was my house I probably would fit a new CU and whilst I was at it split the only ring and lighting circuits with new MCBs for the alarm and external lights. The other difficulty is that the CU beneath a window seat in the lounge (1900s house) and access is very limited without destroying somebody's hard work. I'll leave that to someone else

I will stick to grabbing the socket ring in the understairs cupboard as I need to change the wiring to a bell transformer (that's wired on the lighting circuit) so can kill two birds with one stone.

PS I have a copy of the 16th Edition on order from the library so should make for interesting bedtime reading.