When I took my B+E test a few years ago, the instructor told me that if a trailer has a MAM of 3500kg, then a car that can tow 2800kg MAX cannot legally tow it, even if the trailer was unladen (say for instance the unladen weight was 1500kg, well within the cars capabilities).

I have tried finding this information on line and cannot find this rule anywhere. I am asking because I occasionally need to tow, but am thinking of getting a vehicle that has a max towing capacity of 2500kg, but the trailer I have has a MAM of 3500kg (but I would only put 1000kg max on it and the unladen weight is 1000kg).