Bs 61009 are RCBO’s…. I doubt the trip time for each individual RCBO was exactly 33ms for each one.
Can we get a photo of the CU with the lid open showing the breakers?
We might find they’ve taken a blank out to fill in the hole in the top
got home and had a look they’re mcbs 60898
Turned off (kitchen sockets) whole of downstairs went off

Ill have to get my tester out on the weekend and test everything
makes me worry haven’t even scratched the surface