Trailer towing requirements
A trailer is anything towed by a vehicle. So caravans, cattle/horse boxes, car transporters etc. are all trailers. So is a broken down car towed by another vehicle, and the driver of the towing car usually needs to hold a B+E licence.
Drivers who passed a car test on or after 1 January 1997 are required to pass an additional driving test in order to gain entitlement to category B+E which allows them to tow trailers with a maximum authorised mass in excess of 750KG.
Category B Licence (for tests passed on or after 1st January 1997): Motor vehicles with a MAM (Maximum Aurthorised Mass) not exceeding 3500kg having not more than 8 passenger seats with a trailer up to 750kg. Combinations of towing vehicles in category B and a trailer, where the MAM of the combination does not exceed 3500kg and the MAM of the trailer does not exceed the unladen mass of the towing vehicle.
Most caravans when fully loaded will be over 750 kg. This limit can be exceeded without taking a B+E test: The laden weight / MAM of a trailer can be upto the unladen weight of the towing vehicle, up to a maximum of 3500 kg in total for the combination.
e.g. Land Rover Defender 90 has an unladen weight of 1740kg and therefore you might think you would be able to tow a trailer with a MAM of 1740kg, but beware that the load capacity of the Land Rover, over 20kg, would put you over the 3500kg MAM for the combination! So as the MAM of the Land Rover is 2400kg you can only tow a trailer with a MAM of 1100kg (If your trailer has a MAM of 1500kg but only weighs 1100kg because it is not fully loaded it would still require a B+E licence).
If you had a Land Rover Freelander weighing 1640kg unladen, with a 2060kg MAM then your trailer could have a 1440kg MAM and would not exceed the 3500kg MAM for the combination and therefore only a category B licience is required. (If your trailer is below 750 kg MAM it can be towed by a vehicle up to 3500 kg making a total train weight of 4250 kg). The only way to be sure is take whatever you are towing to your local public weighbridge and check its weight. You need to know the MAM and weights of the towing vehicle, the trailer/caravan and the combination. Also check the manufacturers plate to be sure none of the weights (axle/nose) or MAM for any trailer are exceeded.