The mystery looks solved. Both villages have large waste or minerals sites prominently visible from the train. One can only assume that cabinet office civil servants did a quick look out of the window whilst commuting site visit and that was it.
Gerrards Cross has a huge landfill site to its West due to close in 2017. Of course it has a full restoration condition so it does not count as a brownfield site.
Yalding similrly has a large sand and gravel site to its south, however the operator has agreed to wind down operations and it was removed as a site from the Kent Waste and Minerals framework, of course it is also in teh flood plain.
None of this makes either site any less silly.