Thanks Tony. The back box has now been changed with no difference. Pipes and hoses will be removed tomorrow and inspected. We still have the donor car in so I expect to get back down there on Thursday to have another look. I think this thing has a variable vane turbo and although it spins freely, I wonder if this could be a problem. Will have a look at ways of testing the turbo pressure sensor/regulator...... and anything else that can be prescribed.
Regards
Pete M
PS. I am told this vehicle has excessive diesel consumption which I don't think has been mentioned before although it doesn't come as any surprise.