I suppose, to a greater extent, they’re relying on voluntary compliance and good sense, as enforcement is next-to-impossible. They’ll make an example of the odd idiot who really takes the mick, but on the whole that’s all they can do.
The research seems to point to the chances of transmission outside being low, so I still think walkers aren’t the bad guys here.
I suspect there will be a lot of full car-parks in the coming weeks, regardless of the strict interpretation of the rules (cough..Barnard Castle..cough), but the recent mountain rescue tragedy shows that you need to be aware of the possible repercussions.