Thank you LM. This is a simple situation and the complexities of towing as part of a business don't need to be raised.
There's a nice short leaflet which sets out the rules
http://www.dft.gov.uk/vosa/repository/Quick%20guide%20to%20towing%20small%20trailers.pdfTo flesh this out I just checked my car's VIN plate which reads
2510 - the maximum weight of the loaded car - it weighs 1760kg empty
5510 - the maximum of car plus trailer - so a 3000kg trailer can be towed with the car at maximum load
1200 - maximum weight on the front axle of the car
1460 - ditto for the back axle
My Ifor Williams 510 has a plate reading
2584 - maximum weight of the trailer
1292 - max weight front axle
1292 - ditto rear axle
I know the 510 weighs 1100kg so I can in theory load two 700kg warmbloods and their hay - as long as their weight is evenly split front-rear, which it won't be. The trailer should be nose heavy by 50-100kg, which weight is taken by the car.
Fully laden this falls within the 3000kg towing capacity of the car even if I've loaded 750kg of fuel, people and iron bars into the car. Not sure I'd want to do a hill start though.
The above numbers will all be smaller for a Freelander and 505 but the principles are the same. Note that the advice not to exceed 80-85% of towing vehicle's weight is a recommendation only. It is highly relevant to single axle trailers rather than the close coupled Ifor Williams twin axles which resist yaw and the tendency to snake which plagues caravans.