We did find him. I threw my coat over him and we took him straight to our vets. When we sai we had a RTA they dropped everything and cleared a consulting room for us.
The vet can detect no broken bones (except prehaps the tail) but although able to stand there appears to be no feeling to the left, back leg and possibly fluid on the left lung. His eyes are clear and bright and the same size (no head injury) but very pale. This might be shock?
They will keep him in and give him fluids, AB's and painkillers and see how he is overnight. Judging by his general state, he is a stray. We can't afford another cat (not just cost but space!) But we could not leave him there - I wouldn't sleep!
I really don't know what the outcome will be. but I know he is in the best place at the moment.
I really would appreciate all your good vibes at the moment, poor wee fella.

Why does this keep happening to us? If ever I needed my Premium Bonds to come up it's NOW!