Fingers crossed that the problem is solved. I have used this mechanic for the last 13 years, and he has always been spot on, not only with my direct family cars but also those of my step brother and his kids too.
it is just so strange, the symptoms don't tie up with the things found while investigating the fault...... the noise has definitely gone, the only thing that my mechanic found were signs of wear on a single tooth of a gear in the rear diff, how that causes a loud, and I mean loud "CLONKING" noise that varied with regard to speed that the car was moving just doesn't seem right. Anyhow, I will let you know how things go after a few days of driving around. You never know, this might help save someone a few quid later on.