In reply to Ramon Marin:
Incorrect. A camper van or a vehicle equipped for sleeping, or a motorhome can be classed as a ‘caravan’ and thus cannot willy nilly be parked anywhere overnight, without landowners permission. A public road is owned by the council and some councils specifically prohibit this in problem areas. I would imagine Portland is one of those areas.
’illegal’ maybe not criminally, like trespass, probably just a civil offence but something a busybody could give you hassle for.
It’s so easy to drive off the island, respect local wishes, and find a nice carpark on the mainland. Sets a good example for everyone else and with the added bonus of not risking having your vehicle keyed or having to move at X:YZam.