The 3 ton ULW Bedford TK

When did it change to car licence up to 7.5t gross ?.That’s what I always worked under but I knew there had been some sort of different rules based on the 3 ton UW before that.Don’t know anything about about an HGV sub class below class 3 though or why it was needed.While 7 t payload on a 3 ton tare sounds bonkers in that regard. :confused: