White lines don't provide any enforcement rules either, they have no legal status.
If you are blocked on your driveway, the police can move the car, but if you are blocked out, then the police can do nothing, with or without the white line.
police can get involved because a law is being broken, obstruction it is, though as for getting in its a local authority incident, remember no one has the right to park on roads only the right to use them as thoroughfare if tax is paid. if some parks over a dropped kerb then take a pic and send it to the council who then get, parking enforcement to issue a ticket, a white line serves as a visual reminder not to park there