On Wednesday, 15 May 2019 17:15:35 UTC+1, Tricky Dicky wrote:
I do want discrimination in the garage ...
Is there any reason why the garage circuit cannot be protected by
an RCBO at the house CU

Yes, discrimination.

AFAICS no time-delay / 100mA RCDs are available as RCBOs, so you'd need to allow for a 2-module time-delay RCD and an MCB for the garage - if they're available in BG.

Also someone will hopefully clarify whether 100mA time-delay is acceptable for protecting buried cable.

Owain