If you passed your test after 1st January 1997, you will not have category B+E on your licence, which enables you tow any trailer up to 3500kg. Without your B+E category you will be restricted in the types of trailers you can tow although there are still towing options available to you.
The leaflet attached give you guidance on what trailers you can tow, depending on your towing vehicle.
Alternatively, you can sit your B+E towing test. As of December 2009, tests cost £110 but like your driving test, prior tuition is recommended. The NFU provides B+E test and training discounts to its members.
There are tuition and test centres located acorss the UK.