You'll probably find that the terms and conditions for use of the car park exclude liability for injury, unless by virtue of negligence on the part of the employers. That's a legal provision; one cannot contract out of liability for death of a person, or property damage by negligence under the Unfair Contract Terms Act.
I'm sorry to hear of the injury, but from a purely legal view, there really isn't any liability on the employer's part here. The liability (should there be any) is potentially with the driver of the vehicle, but suing him/her could lead to a very strained working environment!
I like the idea of the term 'reckless' being used by some on this thread too- how on Earth can you possibly know that?? That kind of thing is for a lawyer to argue if you pursue it. Also, I'm with Ummm and Buildersmate on this one- and I'd be wary of taking my advice from someone who can't even use a full stop or spell...