You have misunderstood or - more likely - they have poorly explained it.
I believe on the information you give that your licence is post 1997 but pre 2013 so your entitlement is you may:
- drive a vehicle up to 3,500kg MAM towing a trailer of up to 750kg MAM
- tow a trailer over 750kg MAM as long as the combined MAM of the trailer and towing vehicle is no more than 3,500kg
MAM is also known as Gross Vehicle Weight.
Funny you should choose a Land Rover as your example. In the case of my RRC (1986 3.5EFi automatic) Land Rover give its GVW/MAM as 2510kg.
With my car you can tow a trailer OVER 750kg (which must be braked) up to a MAM of 990kgs (2510kg + 990kg = 3500kg).
If you have a vehicle with a MAM of 3500kg you can tow a trailer with a MAM of up to 750kg as the legislation permits you a combined MAM of 4250kg.
The 3500kg is Land Rovers figure for the maximum weight of trailer so even on my licence I can't legally exceed that weight with an overrun braked trailer. (LR give a higher weight for coupled brakes)
Confusing isn't it!
Personally I never saw the point in the messing about with the legislation. If there is believed to be an issue then from a set date legislation should require that anyone who wants to tow should pass additional training.
Apologies to the OP for the hijack!