As you probably know, drivers can't park in front of a dropped kerb because it's classed as an obstruction to driveways and to wheelchair users, cyclists etc trying to get off or onto the kerb. However, when it comes to white lines it's a little different. White lines are used to discourage people from parking there, but it's not legally enforceable. You can only request an owner to move their vehicle but that's about it. So, as long as a private driveway or dropped kerb isn't blocked, it isn't illegal to park on the solid white line outside your house.