put simply
your unladen weight of tow car has to be more than fully laden wieght of trailer ie
tow car = 1300kg unladen
trailer weighs=1299kg fully laden
AND the FULLY laden GROSS weight of tow car+fully laden weight of trailer doesnot exceed 3500kg
That's how I read it too, though it would appear they have changed the rules from 1st jan this year to mean you can't tow anything over 750kg full stop