Local authorities have a statutory duty to hold stray dogs  for seven days so missing pets can be reunited with their owners. If the dog is not claimed after seven days, the authority can find the dog a new home (usually through a rehoming organisation) or euthanise them.

Anyone who finds a stray dog must make an attempt to reunite them with their owner if they know who they are, or report them to the dog warden if they do not. The police are not responsible for stray dogs in England and Wales. If you still have the dog under your care before or after contacting the dog warden always ask anyone trying to reclaim the dog for Identification and proof of ownership if they contact you . NEVER give a dog to anyone without this . 

If you find a stray dog and wish to keep them , you must still contact the dog warden first. If you do not, you could be accused of theft. If the dog stays with the finder it has to be kept for at least 28 days and cannot be rehomed be the finder during that time  . 

Law: Environmental Protection Act 1990