A local trader parked and left his unattended, small van in a local lay-by in order to advertise his business, which is emblazoned on the side of the van. Although the van was parked inside the lay-by (so not poking out into the road), it was parked perpendicular to the carriageway, presumably to maximise sight of the trader's business details. This lay-by is a school bus pick-up point for my daughter on this rural road with a 50mph speed limit. The trader's van meant the school bus could not stop safely this morning; in effect the parking of the van made the lay-by half as long as it would otherwise have been. I wrote an email to the trader with attached picture and suggested he was risking the safety of others as a consequence of his actions. He wrote back a rude email stating he had a legal right to park in the lay-by and in the perpendicular orientation as well. Is he correct about his legal rights?