It does stretch the definition of 'free at point of delivery' just a tad, doesn't it.
Unfortunately in many cases I think the Trusts have sub-contracted the parking arrangements and there's not a lot they can do without taking on the burden of paying off the contracts themselves. Even in Scotland, where hospital parking is meant to be free, there are a couple of places where private companies have been allowed to build car parks in the hospital grounds and there are now contracts in place that mean those companies are entitled to continue to be paid for cars parking there.