I don't think there is a right/wrong for far right switch, other than how the manufacturer intended it's installation in that CU.Oh my word - how did I miss this, I can see the reason for the 2nd main switch !! See photograph below. I'm right the far right MS2100 switch is connected the wrong way round, and the tails are then connected in reverse to the middle main switch to correct the polarity, which is why I didn't pick it up. You can just see at the top of the MEM switch the Neutral is in the Line and the Line is in the Neutral
The middle switch had to be connected that way around as presumably the bus bar has a leg in the Line at the bottom and needs to extend to the right.
So I don't think anything has incorrect polarity in practise, other than the markings being backwards on the middle switch.
Sounds like a plan, but I'd IR test each circuit first, L+N to earth to find any potential issues when circuits become RCD protected again..Found what this board SHOULD look like. I'm just wondering if I should just get one of these, rip the inards out of both, and put the inards of this one into the one in the wall, and not faff about trying to rewire or understand the mess.