I would like to modify may previous answer a little.
As Raywood points out, the BE test has certain stipulations regarding size and type of tow vehicle and trailer to be used for the test. Generally if you use a towing school they will provide the required equipment, how ever you can simply apply for your self.
You will find the basic specifications for tow vehicle and trailer here
https://www.gov.uk/car-trailer-driving-test/trailer-rules
BUT - I must warn you that these pages on the Government portal have been found to contain errors, and I have not scrutinised these relevant pages in detail.
I did suggest using a trailer of similar size to your caravan for practice, and the reason for that is the longer distance from the coupling to the trailer road wheels, the slower (and thus easier) it responds to steering input when reversing. However, as you need to be able to pass the test with the specified trailer type, it may be better to practice with the test size trailer.
Generally speaking if you can manage reversing a shorter trailer you will find a longer trailer easier.
The towing test is not just about reversing, it also covers correct hitching procedures, and other good safety aspects,
I would venture to suggest that even those older drivers who already have Cat BE and intend to start towing may benefit from having some professional towing training even if you have no intention of taking the new test. The caravan clubs used to offer such courses, and may have commented on how useful they found them.