I think the car handbook has the MAM (sometimes called Gross Train Weight), which is derived from maximum car laden weight (GVW- Gross Vehicle Weight) plus trailer and load weight (GTW - Gross Trailer Weight).
The car will also have a stated max towing capacity (750kg for unbraked and as stated for braked). The Disco/RRS/FFRR have a tow capacity of 3.5T and ISTR the Freelander was less.
The trailer itself will be plated with a maximum Gross Trailer Weight (GTW) which is the max allowable weight of trailer including load (boat, fuel, kit, picnic et al).
If you're pulled over by the police/VOSA you'll be in the brown & smelly if either the MAM, GVW, or GTW is exceeded.
BSAC have a good guide to legal towing on their website.
Hope that helps?
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