I just looked now....
All the plugs ironically now appear normal. I did clean them earlier, and have only driven about 20 miles since, but as I say they *look* ok. (greyish/brown and dry)
I took the
box out and checked everything was clean and well connected (all the ht lead connections looked good, and there was an electrical connection which also looked ok). The box itself seems to be a sealed unit, so I can't take it apart and fiddle with it.
Put everything back again, but still the same....
Whaddya reckon mate? New plugs, leads and black box? Then at least if that doesn't sort it, I know it's not them