An update.
Wastegate actuator was completely seized so a recon turbo was the only option.
Apparently removal was difficult as everything corroded in place.
As a result, a bill of £1000 at a turbo specialist and I think they were honest with me.
Secondary result, complete disillusionment with turbo diesels and Fiats with any high-tec components (I would still happily live with, for example, a Panda 1.1 Active!).
So, looking forward to delivery of my base model, petrol-engined, 4WD Dacia Duster in the new year.