Ok, thanks guys, I need to do some investigating.
The engine it actually in a vw camper van - 1986 t3. So is canted over at 50°.
It is not an unusual conversion, but you have to use a sump and oil pickup off a jx diesel engine (from a t3) and it is a great engine for a van, lots of grunt!
I don't have any oil pressure lights on, but am wondering if the oil pressure is low - so I will have to check.
I will also blow through the oil/water cooler to check that is not blocked.
Thanks for the help - let me know if you have any more ideas.