On 04/10/2019 18:56, George Miles wrote:
Is it OK to use 1.5mm for most of a lighting circuit,
including all the shared feeds,
and 1mm 2 core and 3 core for some individual lamps and switches?


Yes. Subject to maximum loadings, MCB rating and installation methods.

All of which is probably irrelevant on a domestic property with a 6A MCB.

--
Adam