Story has a happy ending after all. Had him over, he terminated the earth wire behind the switch and removed the strap which was connecting to the other switch, if I want to return it back to its original state it is easy enough, unscrew and screw it back. He connected the neutral wire from the 4-core into the junction box in the loft above the light fitting, so it's using the same neutral as the light itself. Whole job took around 40 minutes including a cup of tea and that included removing the light fitting, adding a new wire in and going up the loft.
He did mention that as far as jobs go, this one was on the easier scale. So I can imagine this gets much harder in other cases.
Had a look again at my breaker box, no RCD (googled, so i had a fair idea), however there is a Square D main switch next to it disconnected. Sounds like a rattle to be honest. Not sure how I missed it. I guess this is what they replaced with the Protek?
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