perhaps with over run, though there are other methods...
saw section on direct gov other day, can't now, typical, though
did find this in relation to new regs from 1 jan 13
Category BE
If your trailer weighs over 750 kg and the combined trailer and towing vehicle weight is more than 3,500 kg, you’ll need to pass a further test. The trailer you tow must not be heavier than 3,500 kg. This test will be shown on your driving licence as category BE.
Category C1E
To tow a trailer weighing more than 3,500 kg with a car or small vehicle (category B), you’ll need to pass a test for category C1E.
So note there must be some sub 3500kg vehicles with option to tug more.
even though i agree typical car gross trains are based on 3500 mam for trailer.
I'm thinking these mini fifth wheels where in a sense you are not just towing
but also carrying a large nose weight. so trailer weight is over 3500. the trailer
axles carry so much of its weight, the tug the other.
theres also a section saying there are no ratios of weight for BE class, so 85%
is only a recommendation as is usually more than enough for a caravan a flat
bed or tipper trailer is easy to get to say 2800kg for a terrano, or 3500kg for
a patrol.
ironically a vosa leaflet extols the virtues of 85% for all trailer types.