After lots of diagnostic time I decided to go ahead and fit a new pump (or get a mate to!), exactly the same, F@?!*. Did a complete point to point wiring check for the whole system, I'd just checked bits before, found nothing wrong. Finally bit the bullet and fitted a new ECM. Started and ran first time. Total parts cost...£1321 inc vat to the customer, I doubt if the whole thing is worth 800 quid, wish my crystal ball worked better, I would have got the customer to scrap it! FWIW. the new ECM ran straight away,no coding, obviously comes in new born mode and accepts whatever vehicle it is put into. It only remains to write the bill up!