I think confusion may be caused by the NEC's "whats on" listing showing an £8 parking charge for this event. As the NEC website appears to be as yet unaware of the following month's OS Outdoors Show (for which I believe the parking charge WILL apply - stand to be corrected), I would tend to consider the information in Ratty's link to be correct.
They've charged £7 parking the last few times I've been to the commercial vehicle show but entry to the show is free as long as you register.
Last time we went to the outdoor show there were signs displeyed with parking charges on them, I believe these were for another event taking place at the NEC at the same time.
I hope we see confirmation of this before I buy tickets, if they're charging parking & entry then we won't be going. Having to take out a second mortgage for a sandwich or sit on the floor to eat food you take from home is bad enough.
If anyone's still in any doubt, Customer Services at the NEC have responded to my e-mail of yesterday confirming that there will be NO CAR PARKING CHARGES for the Boat and Caravan Show (but charges will apply, as I suspected, for the Outdoors Show.