From what I can see, there is no region data that matches Groundspeak's regions. They do have a region layer, which seems to be the same as in Openstreetmap. For UK itself, the only difference is that Southern England is a part of South East England according to this and OSM. Groundspeak has them seperated.
The same follows for Scotland and Wales. They are divided into North/South by GS, but not in OSM or the above.
Here follows a list of regions according to Groundspeak, those that begins with an explaination mark doesn't exist in OSM, or in the data you linked.
! North Wales
! Northern Scotland
South East England
! South Wales
South West England
! Southern England <- Part of south east in OSM
! Southern Scotland
Then you talk about "County, Unitary Authority and Metropolitan". These are the counties, and it's probably the case that if one joins the correct counties, one will get regions that matches Groundspeak's definition of regions.
We have not this far worked with joining polygons into bigger ones, and don't have much technology for it in place. Which means a lot of work.
Ideally for us, is when matching data exists in OSM, which is true for most (west world) countries.