Hi All, thanks for your welcomes and useful comments.
Swarfy, thanks for the analysis. You are probably right, (Looks like I didn't get away with it).
It does run really well with not much piston tinging, probably because there's so much oil around in the lower bores. I'll investigate along the lines you highlighted ref oil filter and scavenging etc. Oil filter is in the line before the T. Pick up/scavenge pipe ball valve appears ok, ball is where it should be and free.
Previous owner did run it without an air filter so its possible that the bore & piston scoring I discovered was caused by that. He also had it running far too rich, biggest main jet I have ever seen in an A10! As you said, very effectively washing the bores!
Hoping not to have to reline but at already +.060 if I remember rightly going to +.080 is a probably not a good idea on an A10?
Groily, your idea ref a hidden head crack (expanding as it heats) could be an explaination for the increasing blue white fog. I'll look for cracks during the investigation.
Also changed fuel in case there could be contamination, that would have been a really easy solution, (why is it that life is never that easy!)
My gut feel right now is that this is going to end up being a perfect storm of contributing causes.
Yes, a full stripdown and investigation will be my next course of action.
Our friends in Wales are going into a full lockdown today so my conversation with SRM will probably have to wait. My engine problems are but a drop in the pond compared to what they are having to put up with.
Its great having access to some fresh perspectives, its like the old saying 'when you are up to your a...se in crocs, its easy to forget that your primary objective was to drain the swamp'.
Any more ideas that you can come up with are welcome, I will keep you all updated on any further progress as it happens and as I investigate your ideas on a cause.
Thanks guys,
Dan.