Caravan detaches whilst towing.

Looking on unsurance sites, I did come across one which said the caravan/trailer was covered for Third Parties, whilst attached to the vehicle.  This has led me to wonder who pays out in such an incident; does the vehicle insurance still hold good, or is it down to the caravan insurance policy?  What happens if the caravan is not insured (possible with older vans)?

There seems to be very little advisory detail readily available for this subject, insurance policies are very sketchy despite the popularity of towing, and I believe it is in all our interests that a definitive answer can be reliably obtained. 

Ignorance is not always bliss!