Fitting a combined remote control fan and light, in the living room[1}, plus firing up immersion heater, electric heater, washer, and dish washer - to make use Octopus's two hours of free power, announced yesterday, beginning at 12:00. We got it all set up, ready to go, took the lampholder/ceiling rose drop down, went in the workshop, started making up a timber spacer for the fan, switched the saw on and the RCD tripped.
Back in the house, reset the RCD, saw tripped it again, restarted all the appliances, started the saw, it tripped again. Tried to reset it a third time, and it wouldn't reset, so tried it with all circuits off. It reset, so tried adding the circuits back one at a time, and found it tripped on the downstairs lighting circuit. Parted two blacks, at the living room ceiling, and it then didn't trip.
Now, I just waiting until 2pm, the end of the free power period, before investigating further.
[1] We bought the same remote fan/light unit some while ago for the bedroom, and it has been great - and so decided to buy a second one for the living room. Problem was, the living room ceiling light, has a large plaster ceiling rose on it, so the fan unit, needed to be spaced down to clear the rose, with a made up bit of timber packing.