Well, I'm not sure if it is an escape artist or its owners just let it wander out and about but there is a dog who I've seen numerous times over the years out on its own, both during the day and at night.
It doesn't look to be a stray at all and looks like a pedigree type of dog, like a shar pei I think, big and wrinkly.
It seems to have a thing about my front lawn and there is often dog poo on there which isn't pleasant. It also seems quite aggressive and not a dog I'd go near. It's usually tearing up the grass and snorting about and doing its business. I have reported it to the Dog Wardens before now but they've said they cannot do anything out of hours unless the dog is contained (had it with other dogs on the loose too).
It's a possible danger to itself and to others, people and motorists. I've even seen it square up to a massive Bull Mastiff who was thankfully on a lead but the walker said he wouldn't be able to restrain the dog if it wanted to go. You can also hear dogs in the area barking when it's about. Do the Dog Wardens have any kind of responsibility to try and find owners of dogs who are regularly out on their own?
Can you get a photograph of it? I would contact your local newspaper they might be prepared to investigate where it comes from and who owns it and why they let it roam around. Your local councillor might be able to chivvy up the dog wardens too.
It is the Dog Wardens job, ring them during the day and tell them you are going to report it to the police, if you see it again as you are frightened to go out when it is there. The police should take action if you report that the dog frightened you. However it depends on how you feel about the dog being put down if it is seized for being out of control. Hopefully the Dog Warden should arrange for it to be picked up as a stray and retained for seven days for the owner to claim it. Then it can be rehomed or put down according to its temperament.