I spoke to VOSA earlier to clarify the situation regarding having a tow bar/hitch on a Land Rover and using it for business use.
The long and the short of it is thus:
A passenger vehicle which is also used as a towing vehicle is described by VOSA as 'combined use' and comes under the same regulations for towing as a goods vehicle. On this, my earlier comment was incorrect.
However, an offence is only commited when the gross laden mass of the vehicle train (i.e. towing vehicle and any trailer) exceeds:
Business use: 3,500 Kgs (exceptions include not being used more than 50kms from the registered address of the vehicle and carrying tools or equipment required for the profession of the driver where driving the vehicle is not the drivers main job and the 'train weight' is less than 7,500Kgs)
Private use: 7,500 Kgs
Having the ability to tow a trailer is irrelevent, as, if no trailer is attached and the actual vehicle weight is less than 3,500 Kgs, no offence has been committed.
If you use a vehicle of less than 3,500Kgs laden and it is fitted with a tow bar, but you never tow for business purposes you do NOT need a tacho fitted.
If you use a vehicle of less than 3,500Kgs laden and it is fitted with a tow bar, but you only ever tow for business purposes a trailer which does not, when laden, cause the combined weight to exceed 3,500Kgs you do NOT need a tacho fitted.
Just to reitterate, it is the ACTUAL weight of the vehicle and any trailer at the time of any alleged offence which is important, not the maximum permissable weight or towing weight of the vehicle.
Example: Land Rover Defender 90, car fully laden to manufaturers maximum weight = 2,400 Kgs hence no tacho required. Exceeding the conditions of use regulations for over loading a vehicle is a seperate offence. You can still tow a trailer of up to 1,100 Kgs laden weight without requiring either a tacho fitted to the car or an operators licence.
I don't know the manufacturers figures for a Disco, but it and the individual axles weights are listed on the VIN plate under the bonnet. If it's in the same order that mine is the list is:
Maximum gross mass:
Maximum gross mass including trailed load:
Axle 1 (front axle) mass:
Axle 2 (rear axle) mass:
Hope that clarifies it a little.