That was my conclusion after reading replies... At least I can ask that directly of the tyre shop and see what they say, with the benefit that they can see the damage and the object (I kept the screw)... Armed with knowledge, so to speak...
If I were single and the only one driving the car, I wouldn't worry much either. I'm paranoid because of my family - it does that to a man ;->
I used to fix my own cars all the time (head removal, brakes, electrics etc) - with the family and lack of time, I've been out of the game for 5 years, so my mechanical judgement has gone to pot... Must do more jobs myself to get me confidence back.
Cheers
Tim