Behind your 2.1 ton Discovery it appears you can legally tow 1.4 ton trailer & load = 3500kg - heavier & you need to upgrade your license with the trailer test.
there are two things here:
Driver restrictions - when did you pass you test?
Sounds like your son will hit the driver limit for MAM above (3500kg)
Licences issued from 19 January 2013
From 19 January 2013, drivers passing a category B (car and small vehicle) test can tow:
- small trailers weighing no more than 750kg
- a trailer over 750kg as long as the combined weight of the trailer and towing vehicle is no more than 3,500kg (3.5 tonnes) Maximum Authorised Mass (MAM)
If you want to tow a trailer weighing more than 750kg, when the combined weight of the towing vehicle and trailer is more than 3,500kg, you’ll have to pass a further test and get B+E entitlement on your licence.
You’ll then be able to tow trailers up to 3,500kg.
Licences held from 1 January 1997
If you passed your driving test after 1 January 1997 and have an ordinary category B (car) licence, you can:
- 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
For anything heavier you need to take a category B+E driving test.
Licences held before 1 January 1997
If you passed your car test before 1 January 1997 you’re generally entitled to drive a vehicle and trailer combination up to 8,250kg MAM.
This is the weight of a vehicle or trailer including the maximum load that can be carried safely when it’s being used on the road.
You also have entitlement to drive a minibus with a trailer over 750kg MAM.
AND -
Vehicle restrictions - each vehicle has a manufacturer's towing weight clearly indicated online and in the handbook
just because I have a pre-1997 license does not mean I can pull a 6000kg trailer with my ford focus!!
your disco has a rating
Discovery - Vehicles - Land Rover UK
BUILT FOR ADVENTURE
With the capability to transport the driver, six passengers and their luggage, and a towing capacity of 3,500kg Discovery is every vehicle you’ll ever need.
Land Rover Discovery (98-04) 2.5 Td5 ES 5d (7 Seat) - MPG, Dimensions & Performance | Parkers
[TABLE="class: verticalTable, width: 325"]
[TR]
[TH]Unbraked Towing Weight[/TH]
[TD]750 kg[/TD]
[/TR]
[TR]
[TH]Braked Towing Weight[/TH]
[TD]3500 kg[/TD]
[/TR]
[/TABLE]
FYI its less for Land cruisers at 3000kg and interestingly even less for a Hummer at 2000-2500kg!
Breach either of those limits and you are liable to be prosecuted if caught, involved in an accident etc etc
AND
your insurance company will have a field day
most insurers want to know if you will be towing anyway
ALL of them will laugh in your face if you are proven to be over limit when you attempt to claim