This might help:
http://www.direct.gov.uk/en/Motoring/Dr ... DG_4022547
On my licence, I've got
B
B1
f k p Code 122
B = Motor vehicles with a MAM not exceeding 3500kg having not more than eight 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
B1 - Motor tricycles / quadricycles, three or four wheeled vehicles with an unladen weight not exceeding 550kg
f = Agricultural tractors
k = Mowing machine or vehicle controlled by a pedestrian
p = Mopeds with an engine capacity not exceeding 50cc and a maximum design speed not exceeding 50km/h
Code 122 - valid on successful completion: Basic Moped Training Course