as qrty sais really,
in those instances that's what the plates are for mate
this is why your land rover can do this, its been tested and is safe and capable, and artic's etc are designed to do that job, and also have BIG air brakes and lots of torque to cope with any drama if need be,(the shape of an artic also plays a big part, it cuts trough the air and the air rushing past keeps the trailer more stable, where as this is diff in a car as itll most likely be smaller or bigger then your trailer in shape terms) but still nothing saying theyll stil cope in an emergency
your average pcv (car) will not, so you have to be careful, if you have a car weighing under what your trailer and contents weigh, you run a high risk of an accident, there are ppl who run like this for years with no issues, but it only takes one big gradient, one kid to run out... or car to make an emergency stop, and your heavy trailer starts pushing you along the road with your foot welding the brake pedal to the floor, as its too heavy to counter the trailer and the brakes arent capable of stopping it, or if they are the trailer starts to try over take you or forces your wheels to lock and slide, and thats before you get onto windy days etc
if your a driver you should have learned all this yeah? best to stick to the guidlines, keeps everyone safe, and may stop you going to jail if say you kill someone in an accident that possibley wasnt even your fault
guidline is around 85% iirc? may have to check that one.. above this even in normal conditions it can become pretty unstable