Thought it might be useful to share my findings as they come to light.
To recap- having recently bought this car it drove for a month with no sign of any problems, till the low oil pressure came up.
The main thing I have learnt to date is that I should have lifted the plastic engine cover and shone a torch around the base of the injectors. I would have seen seeping engine oil, some still liquid and some baked solid. This is a cast iron guarantee that the problems I have since found are sitting there.
I am still dismantling- but have uncovered;
On removing the sump the oil pickup/strainer was badly blocked up. The pickup had to be cut off because the torx screws are too small and cannot cope with the locktite used in assembly. I was lucky and with mole grips managed to ease the screws out- but I'm sure they were on the point of shearing.
By this stage I had seen evidence of the full service history of this 66k mile car. The quality of work carried out by main stealers and independants alike was/is nothing short of criminal.
Next stage was to strip and inspect the turbo. It is serviceable.
The injectors are out. All have the top oil seal totally disintegrated. All have the bottom copper seal blowing by. One so badly I'm not sure the bottom seal remains.
I have no choice now but to lift the head. If there is any chance of this lump running again the head will have to be cleaned and kissed by an engineering outfit, but I'm not sure that any remain round here.
The only good news is that I have not spent a penny yet. Many hours of sweat and toil though- and still a long way to go.