There are regulations for towing diesel regarding the volume of fuel, the type of bowser and the vehicle towing it. The bowser must be suitable for towing, and the vehicle must also have a suitable weight limit. This limit is often found on the VIN Plate.
When calculating the weight of a fuel bowser when full, use 1 litre of diesel = 0.82 Kg, this sum must then be added to the bowser weight.
Towable bowsers with a capacity of up to 1000 litres may be towed without an ADR licence, however they may require a towing licence dependent on when you passed your driving test.
All fuel bowsers with a capacity of over 1000 litres do require an ADR licence, as well as having a width of no more than 2.55 metres and weighing no more than 3500kg.