You can drive upto 3.5 tons on a car license - even after 1997, but with 3.5 tons you have to be careful you don't go over weight. I'm currently driving mine (6.5tons) on a provisional C1 license. I'll do my C1 test eventually but it's peace of mine to know I don't have to worry much about weight
I think it's worth getting a C1 even just for the future