I was actually looking at towing laws earlier this week:
Licenses obtained on or after January 19th 2013
Drivers who pass their Car (Category B) test on or after 19th January 2013 have futher restrictions to their license surrounding towing. Individuals that pass their test on, or after this date are restricted to towing small trailers weighing no more than 750kg. And are only able to tow trailers weighing more than 750kg when the combined weight of the towing vehicle and the trailer is not more than a total mass of 3.5 tonnes.
Car licences obtained on or after 1st January 1997
Drivers who passed their car (Category B) test on or after 1st January 1997 are restricted to drive a vehicle upto 3.5 tonnes Maximum allowed mass (MAM) towing a trailer of upto 750 kgs MAM. With a combined weight of no more than 4.25 tonnes in total. You are also able to tow a trailer over 750 kg MAM as long as it is no more than the unladen weight of the towing vehicle. This is upto a maximum combined weight of 3.5 tonnes in total.
Car licences obtained before 1st January 1997
All drivers who passed a car (Category B) test before 1st January 1997 retain their existing entitlement to tow trailers until their licence expires. This means they are generally entitled to drive a vehicle and trailer combination up to 7.25 tonnes maximum authorised mass (MAM). They also have entitlement to drive a minibus with a trailer over 750 kgs maximum authorised mass ( MAM).
Copy n Pasted from Bubble Towing..