Update! Electrician dude called out. He had to replace the main RCD. I had done everything else right, had all the plugs unplugged etc, and was able to talk about switches and trips etc. I'm not quite a 60 watt male, but winged the conversation enough to appear like a 40 watter.
€100 quid all the same
Did you refer to him as "a sparks"? That would have convinced him.