Yes, that again. I've done lots of Googling and read the Which?
guide, but I still need some clarification, as the Regs (or at least
the way they've been summarised in the sources I've looked at) seem to
be ambiguous.

On the one hand, they say outbuilding circuits should have RCD
protection.

On the other hand, they say lighting circuits shouldn't have RCD
protection.

So what do you do about lighting circuits in an outbuilding???