Thanks for the updates all,
Clarification on current position :
Outside socket has nothing plugged in, and as of now, nothing is plugged into any socket on the ring!
RCD is working as normal - this one is either on or off, no mid position in my one. My father in law had mixture of user error and not following instructions which led to the confusion of Rcd not resetting : he had reset the MCB first, thet tried to reset Rcd. Fault on MCB caused RCD to trip.
Since Friday I have had one item unplugged at a time until trip. At which point I put the removed item back in, and removed something else. Saturday morning I unplugged an extension (nothing on the end of the extension but it has built in usb charger). Rest of the day, no trips, and all night nothing. This morning RCD and MCB tripped.
Unplugged new device and reset Rcd, then MCB. Stayed up for approx 1 hour, dishwasher started, used toaster for breakfast etc , and both tripped again. Unplugged new device and reset Rcd, tried to reset MCB and it tripped RCD immediately. So removed more items and tried reset of Rcd and MCB. Now I'm at the point where there is nothing plugged in anywhere, the extractor is isolated, and even the fused switch spur for outside is disconnected (load side for l,n and e) so as far as I can tell, 0 devices plugged in), yet RCD trips when MCB is turned on...
Funnily enough this is what my fil described happening on Friday morning, RCD won't stay up when MCB is up! So I'm suspecting something possible environment such as heat (ufl comes on in the morning to get room warm?) + bad connection somewhere causing short... Going to have to disconnect circuit at consumer unit side to test continuity and possible shorts I suspect as next step!
Any other ideas?