Found In Norfolk.

I'd go for the DP switch (or possibly FCU) and L-N reversal option (I've never seen an earth terminal on a plastic 2G plateswitch), Looks to be some heat damage too - was the bottom left red close to the bottom right black when squashed into the box?  Maybe a loose connection on the bottom right terminal? I can't tell what's happened with the c.p.c.s  maybe caught up in some arcing or just corroded.

   - Andy.

I'd go for the DP switch (or possibly FCU) and L-N reversal option (I've never seen an earth terminal on a plastic 2G plateswitch), Looks to be some heat damage too - was the bottom left red close to the bottom right black when squashed into the box?  Maybe a loose connection on the bottom right terminal? I can't tell what's happened with the c.p.c.s  maybe caught up in some arcing or just corroded.

   - Andy.

I believe that the damage was caused by overheating of the conductors, either by loose terminals or a failing switch. I believe that it controlled a shower or some other heavy current appliance.

Z.