Many local authorities ban the parking of anything over 3.5 tonnes gross weight overnight. It sounds from your description as though this vehicle would be at or under that weight, making it legal. That said, if it's parked in a designated turning area then it may well be said to be obstructing the highway and the police might be interested. (Well, you could try). Other than that, a quiet word with the driver if you can find him might help. Or wait until it's gone and all park your own vehicles in its way.