Before you start, just in case, do make sure whoever is driving has the right groups on his or her licence.
https://www.gov.uk/changes-to-the-driving-licence-and-categories
I know it may sound like teaching a grandmother to suck eggs, but I spent 20 years in the truck rental industry and I lost count of the number of people who turned up believing they were qualified and weren't. I've had people crying in my office because they were expecting to move house / go on holiday and didn't have the correct licence.