Is the parking space on the highway and maintained by the council?

They may have a TRO in place that prohibits vehicles of a certain size parking in the space, or one that prohibits things such as vehicles that are being lived in, used to run businesses etc - they can be very specific as to who can and can’t park in certain places even if it’s not for example a permit bay or disabled bay etc. The council I used to work for technically only had one space in the whole of the city where a caravan could park legally.

Calling the council may be a good place to start - they can then ticket the caravan if it does go against any of the regulations in place and eventually have it towed away if the tickets didn’t deter them.