I don't know. Most mtDNA tests are low resolution (HVR1 and HVR2), which makes it pretty much useless for close regional comparisons inside Europe. Once there will be some big studies (over 1000 samples) using only full sequences from the UK, Benelux, Scandinavia and Germany we will have a clearer picture. I don't expect to see it before a few years though. DNA tests are still very slow and full mtDNA sequences still too expensive to be popular.