Reply from the finder:
Dear Sam
Thanks very much for your response. We have a vet just around the corner from us, but catching the cat is proving to be rather difficult. Last night when I got home from work, he was inside our house, but is unapproachable. My husband will be home later and we will try to get him to the vet. We have asked around. We are finding at the moment that our own cat is accepting the cat, and allowing it to eat his food, which is commendable, and while we do not want to see it out in the cold we do not want our own cat to go hungry.
I will let you know if we get anywhere with the vet
Thanks
Margaret