[Neil]

Legally dogs in a public place must have a collar and a tag with the owners name and address on it. It's logic and shouldn't need to be law. Our two always have a collar on and their tags also have both our mobile numbers on.
The last 2 I found on the street had no collar. I found the owner for one and gave the second to the dog warden. I could just have made a phone call and reunited them both if they had spent £2 for a tag from ebay