Found In Norfolk.

More info needed - looks like either it shorts red to black when on - could be dual gang light switches, or if the reds and blacks are paired the other way, perhaps it is a D-P switch configured as a combined isolator and  L-N reversal(;;) . And one of the blacks is scuffed and would benefit from some  site applied insulation or trimming and re-making. Are CPCs removed for clarity in the photo, or were they actually missing ?

and is it M or 3 that is the cryptic blue mark. ;-)

Actually I think there is a lot of this sort of thing, not just in Norfolk, a colleague of mine had a mystery isolator on his kitchen wall that after much head-scratching was wired to either break or complete the ring final - so on some days it passed its tests and not others. In the end we assumed it must have been refitted wrong by the kitchen tilers. Confusion was not helped that his wife switched it on on laundry days and off otherwise, even though it had no effect on the washing machine.
Mike

More info needed - looks like either it shorts red to black when on - could be dual gang light switches, or if the reds and blacks are paired the other way, perhaps it is a D-P switch configured as a combined isolator and  L-N reversal(;;) . And one of the blacks is scuffed and would benefit from some  site applied insulation or trimming and re-making. Are CPCs removed for clarity in the photo, or were they actually missing ?

and is it M or 3 that is the cryptic blue mark. ;-)

Actually I think there is a lot of this sort of thing, not just in Norfolk, a colleague of mine had a mystery isolator on his kitchen wall that after much head-scratching was wired to either break or complete the ring final - so on some days it passed its tests and not others. In the end we assumed it must have been refitted wrong by the kitchen tilers. Confusion was not helped that his wife switched it on on laundry days and off otherwise, even though it had no effect on the washing machine.
Mike