In the boiling hot July of 2006 - 10 years ago - I actually smashed the window of a car left near the canal, as there was a dog inside, and the car was in full blazing sunlight at about 3pm. It was well over 30 degrees in the shade, so God knows what the inside of the car was like. Anyway, I reached inside and opened the door, the poor dog whimpered his way out, and laid on the ground, panting like hell. I immediately called the police on my phone to tell them what I'd done. They came out about 30 minutes later, accompanied by the RSPCA, took my details and said something like "OK mate, we might need to talk to you again". The RSPCA took the dog away, and the police were checking on the vehicle itself. No sign whatever of the owner. I then walked home. I'd wanted to give the dog some water, but didn't have any, so poured some cold coke on him in the hope it would cool him down a bit. If he'd been left much longer, he'd have been a goner.
All this time I'd half been expecting the owner to return and attack me, or to get arrested by the police for malicious damage. But neither. Somewhat surprisingly I never heard another thing.
I agree with you, Pete. If you can't look after a pet, don't have one.