Scott
Graham here used to be a tour guide at MMC so he will have more information on that side of things.
The choice between train and driving is a personal one. If you want a nice relaxed trip , then train every time. There are (or certainly used to be) direct trains from Paddington station in London to Malvern Link (closest to the factory and within walking distance)
The route by car is OK, but with the switch to RHD, a strange rental vehicle etc, I would personally be wary of this option unless you are very confident about driving in UK on the other side fo the road, and need the flexibility once in Malvern (other visits etc )
