Gets a bit tricky doesn't it Comes back to this definition of "Congested area".
There's a subtle difference between the way this is handled in US and UK law. The FARs simply require you to be able to land without hazard to persons or property if a power plant fails. You might well be able to justify landing in a park.
The UK however requires that you are able to land clear of the congested area itself. I get the impression that
congested area is intended to represent the entire area of a city or town, not a patchwork of individual squares within the town that are or are not more heavily used. A park surrounded by houses is probably still part of the congested area.
But of course it's up to the judge...