North sea and Atlantic/Western Euro are similar clusters. The guy who runs Eurogenes says that North Sea is basically a version of 'South Baltic' altered by gene-flow from the Atlantic, South and Central Europe. Where'as Western Euro is pretty much the same but altered a bit more than North Sea. So all NW Europeans will have large amounts of both. In many cases when the North Sea category is a bit broader, the whole of Britain will be dominated by it (and Atlantic becomes more common in SW Europe i think) but in ones like EUtest there are divides within Britain, with the Welsh and Irish being dominated more by Atlantic, and English more by North Central Euro/North Sea.