I'm based in England and I think there's a misrepresentation of regionality in the search filter for United Kingdom.
The search says GB (Great Britain) and as a result is missing out returning UK (United Kingdom of Great Britain and Northern Ireland) prioritised results.
For example, if you search for "Apple" with United Kingdom (GB) as the region filter, it will return www.apple.com as the top result.
If I search with !r: uk appended, it will give me back Apple's UK page as top hit and other UK based results.
I think that the region filter for United Kingdom could prioritise UK as a locale and GB as a secondary locale.
Strictly Great Britain is within the United Kingdom, so I think that makes more sense.