So I took the plugs out of the other 3 easily accessible cylinders and checked both the plugs and the bores.
The plugs all looked fine (all the same as this)
I did a quick boroscope of the 3 cylinders and found a "little" amount of shallow scoring on all but nowhere near as much as on the No 1 Cylinder and I also found that all the pistons had that same "missing" section in the piston crown so thats the design of the piston and not an issue in the No1. Here's a few random pics of the other cylinders showing the same "missing bit in the No2 an No4 and showing some of the bore marks and the No 2-3-4 cylinders.
So I cleaned up fouled plug, rebuilt the engine putting the No1 cylinder plug/coilpack into cylinder 3 to see if they were fine and put the working No3 plug/coil into cylinder 1. Started the engine and there is still a misfire on Cylinder 1 (No3 runs fine so plug/coil OK) and, now I've got bore pics from 4 cylinders to compare, it's pretty obvious that the No1 has 1 if not 2 deep scores about 180' apart so I'm fairly sure it's lost compression
It gets taken up to Unit20 next week so I'll let Grizz take it apart and see how bad the damage is, cry a little and then prepare my anus for the bank manager/Audi!