Oh just noticed this old thread - sorry I'd never responded. :-s
Seems like a life time ago now but basically from what I remember after arguing and arguing, Ford didn't back down. So you'll be disappointed to know that my dad gave up and replaced it himself. (It was christmas time and had went on long enough, and my dad just wanted his car sorted to get on with his job).
I think he'd went to a local certified Ford service place who does a lot of work for a large taxi firm (with mostly Fords on their fleet). They recommended a turbo which was the same as the OEM one, just without 'Ford' stamped on it - for a lot less than £900 - can't remember the price he paid).
Without asking my dad thats pretty much all I remember, and the cars been fine since. He'll be looking into changing it either this year or around March 2015 - probably for a new Fiesta actually as I guess after time passes you kinda forget about odd troubles like this one. Generally the Fiesta is a great little car, and one that is desirable for new drivers to learn in .
(And Kevzs960 - his car has all its service stamps etc, probably pretty close to the recommended time/mileage too, but nevermind).
Cheers guys. Sorry again for the disappointing outcome. lol