In short, it depends on the deeds to your property so we can't actually answer that question definitively. What we will say is that many houses have covenants prohibiting the parking of caravans on the driveway, so you may actually find that the deeds stop you from parking there. As for the neighbour, unless the caravan is causing an obstruction or actually blocking her from being able to see past it when she's leaving her own property, she can't really do anything just because she thinks it's ugly. Obviously everyone has different relationships with their neighbours, but I'd bear in mind that you might want to stay on good terms with the people who you live by. It's also courteous, but not legally necessary, to tell your neighbours that you plan to keep a caravan, motorhome, commerical vehicle etc outside your house if you plan on keeping it there for months or years at a time.