Hi RobH & welcome to the Forum.
There are two definitions for dual purpose vehicles. Yours falls into the first definition by the fact it has 4wd and can carry at least one passenger AND a load or burden of any description.
The second definition is for vans which have been fitted with a second row of seats, and windows to the side and rear.
Lots of testers cannot seem to grasp the definitions, but your vehicle should be tested as Class 4 dual purpose absolutely & categorically.
If you have any further problems I’ll be happy to PM my phone number & explain the regs to your tester.
