So after 72 days and £300 on fruitless attempts to diagnose and resolve the problem, I finally have it solved tonight and car is back on the road. Jason (huttojb) has been fantastically helpful. As a mechanical engineer myself I can spot BS and there's none of that, he is definitely knows more than anyone else about these steering units, forget the reman companies, he really is THE expert.
Only little problem left to fix is that the first clown who played about with the car on his Maxi Elite seemed to delete the keyless ignition code so we still need to insert the key. Tried the 5 secs on/off and repeat trick, but not worked. So will either live with using the floppy key or pay a locksmith.
