This is from the Gov website
Towing trailers, caravans and horseboxes with a car, including the weight and size limits, and what licence you need to have
www.gov.uk
Maximum length
If your vehicle’s
maximum authorised mass (MAM) is 3,500kg or less, you cannot tow a trailer that’s longer than 7 metres.
If your vehicle’s MAM is more than 3,500kg then the maximum lengths are:
- 12 metres for the trailer towed by the vehicle
- 18 metres for the vehicle and trailer combined
- 3.05 metres for how far the load can overhang the back of the trailer (whatever the length of the trailer is)
Maximum lengths do not include the A-frame (the frame that connects your car to the trailer).