Cant remember all thats been checked/done/flushed/etc in the last 2 days, but the result is categorically, that there is nothing wrong with my engine and the fuel from Shell has caused the recent problems.
Interestingly we put some of the fuel drained out into a clean glass jar and there is a) a funny smell - bit like turpentine, and b) there is a bubble of something at the bottom of the jar - looks like something you see in a lava lamp....
My D1 V8 petrol/lpg is now purring like a pussy cat again - cant wait to go for a run in the morning.