Hello Andy,
What AlanW writes is correct, but its not the whole story.
Lets start with your driving licence. If you passed your test before Jan 1997 you should have cat's B+E. This entitles you to tow any trailer up to the maximum permitted by the car manufacturers specifications, which in this case would be 1300Kg.
If you passed you test after 1997, and only have Cat B, then you are legally limited to a trailer that is no more than the kerb weight of the car, and subject to an overall limit of 3500Kg for the combined outfit. (unless the car manufactures limit is lower)
Now the UK caravan industry and clubs have taken it upon them selves to suggest a maximum trailer to car ratio of only 85%, whilst this in my view is a sensible target, it has no basis in law, and no other country makes a similar suggestion.
Forgive me if I am wrong, but I guess that you are new to caravanning, in which case opting for the 85% ratio is very sensible choice, but if that unreasonably limits your choice of caravan, then you might consider going for a slightly bigger van provided it is still compliant with your licence and the manufactures limits.
Consider taking one of the towing courses, which should provide you with some new skills and greater confidence to handle a caravan outfit.