Im not 100% sure on this but will say it anyway and get proved wrong no doubt!!
If its plated at 900 Kgs, depending on your driving licence type, you may have to take an additional test to be legal when towing it.?
Before i bought mine i was really worried about this cos if you passed after 1997 different rules apply. i think if the trailer is plated at less that 750 kgs anyone who passed after 01/01/1997 can tow without an additional test as long as max weight doesnt go over 3500 Kgs (Car, Trailer and whatever is in the trailer)
Over 750 Kgs plated trailer or 3500 Kgs total = another test. of course this is all irrelivent if you passed before 1997.
Ill stop waffeling and get my coat!