That is indeed the case in the UK as I found out when access to my property was blocked by a parked car [more abandoned ]. The police told me I would have to leave my car coupled to the caravan. or find somewhere off the lane to leave it. I could not leave it by itself on the lane.
But are you sure that caravan insurance, which I assume is a UK based policy, covers third party liability whilst it is towed?
I suspect not as it is not the normal UK system, here the car insurance has to cover that, hence the need from now on for that second green card whilst travelling outside of the UK.
Simple enough to set up, but just part of the extra hassle "we" have opted for.