Well good and lovely people, I have an update for you....
Head is now off.... Whipped it off last night, and a few bits and bobs aside like no having the head bolt removal tool (Thanks Bill!), and having some odd fashion turbo - exhaust manifold bolts which I just don't have a socket that will fit, all went very well.
Started at about 8 PM, and by 10.30 we had all the ancillaries off and the only remaining things to do were remove the timing belt and get the turbo bolts of the mani. Timing belt - no problemo. Turbo bolts.... well we finally got all 3 out at 1 AM (after hammering a 1/2 inch 10mm socket on and cracking them with a 3 ft breaker bar).
Let me say at this point, I had been at work since 8, and got straight on the car when home - I couldn't be ***** to take photos!
When I unbolted the inlet manifold, cylinder 3's inlet port and valves has visible oil in which wasn't a massive surprise. The other 3 were absolutely fine.
Had a quick inspection of the block, especially cylinder 3. Plenty of oil in there.Bores look good, no abnormal scoring. Rings on all also look good. Quite happily hold WD40 in the cylinder with no problems so that's been deemed as unlikely. Head gasket appears fine also, no obvious damage, or leaks, or marks of any kind really.
So........that left the head. Flipped it over - And it looks pretty good actually. Cylinder 3's exhaust valves are covered in burnt, congealed oil unsurprisingly, but other than that, it looks cushty to be honest... Valves are all in tact. No obvious cracks.
So. God knows what's up with it to be honest. Something head related I'm pretty sure, as everything else looks in very good nick for an engine which has done 125K. I'm going to drop it in to a local company who will look at it for me, hopefully they will be able to find out what's happened and resolve.