this is a very grey area,because a cat d does not need a vic test to be put back on the road, would you tell a potential purchaser about it, sometimes it is only classified cat d for very minor things,like paint damage,or maybe a minor body panel damage,your insurance company would have known,as it is on the dvla register,but as for the previous owner when selling to you,well i dont know. why did you not do a hpi check on it before you bought it,that would have saved you all the hassle you now have.