Hi, thanks for the reply..!
No, the tyre wear looks ok - I bought the car 2 months ago, and the previous owner had just replaced the front right tyre, not the left. They look ok.
I'm not a mechanic, so don't really know what to look for - I jacked the Z up & there's no obviosu signs of any damage etc. It just feels loose when travelling in a straight line & needs regular minor steering inputs to keep it in a straight line. Be grateful if anyone has any thoughts before I go to my local dealer & they remove £££££'s from my wallet!