When I was looking at buying a Defender recently, I was warned to check the plating, as quite a lot have a higher capacity axle/suspension setup; sometimes this is plated over 3500, sometimes the plate is standard (presumably the higher capability was for use off public roads, eg forestry).
So some defenders COULD be capable and legal to tow the Hobby, if plated appropriately.
The problem seems to be that a vehicle over 3500 requires a C class HGV (now known as LGV) licence to drive it, and if the trailer is above 750, then it requires the C+E licence - which is the one for Artics!
I'm sure there are people with Artic licences that go caravanning, but the current discussion is about ordinary drivers.
Of course a lot of this makes no sense at all - my wife can tow our small van with the Range Rover on her B licence, but if we got a bigger van, she would only be legal with a smaller car - but we are talking about what's legal, not what's sensible!