The CPC I have is because I drive a PCV, however, the it also covers ALL the C & D categories so the course is generic. I did mine on the job, but I know Dave Ives did his so he will know more about commercial providers. If your main job is driving anything in the C or D catgory in a proffesional role, you must now have a valid Driver's CPC. There was a 5 year grace for those who held the catrgories before the the introduction, that has now run out. As Snort says you just have to attend! And it is currently classroom based, ie a waste of space! The result is a little blue card like the solid driving licence, however changes appear to be happening there as well.
Due to time you'll have to do the 35 hours in one hit, then it can be spread over 1 day a year, as long as by the time of renewal you have been registered the 35 hours.