With the map you have linked, I assume that you refer to what we call "counties", and not regions. Our region data is divided in the same way as Groundspeak, to be compatible.
For county data, we have digged around in OSM to find data that matches http://en.wikipedia.org/wiki/Metropolitan_and_non-metropolitan_counties_of_England.
We know and understand that this is a complex topic in United Kingdom, and that there is not one opinion how it should work. We have been using a few different variants, and we believe this one is the best. Regardless of what system we have used, there has been complaints.
We actually have two tickets open regarding this topic. But it takes hours to handle them, so we haven't been able to address them yet.