No it is not legal a caravan or any other trailer it can only insured if it is connected to a towing vehicle which has insurance to cover the vehicle and the trailer/caravan. No trailer / caravan can be on a road unless it is insured . I have the same problem. A house near me has a trailer that they use as storage , it blocks the dropped curb that is designed to give access to the children's play area across the road, this makes it dangerous for kids to cross the road
I have asked them to move it but they ignore me, I reported it to the police but they take no action.