The presence of I2a1b1 in UK at low percentages is weird,since you can not link that with vikings raiding there.
If this I2a1b1 would have been of native population there,how come it remained only in so low percentages?
Maybe some celts that passed over Balkans and Romania took some people of I2a1b1 with them and this is how I2A disles got in Great Britain.
No one knows for sure the time when I2a1b1a* branched from I2a1b1.
The strange thing is that there are cognates between south slavic and celtic languages,I am not refering to those forced cognates written here by how_yes_or_no but to more serious cognates found by scientists.
Some scientists from institute of thracology from Bulgaria said there are about 178 cognates between south slavic and celtic languages,which atests that celts lived sometime together with south slavs.
I also found this document:
http://www.scribd.com/doc/13082475/C...avel-Serafimov
Some of the cognates here seems forced,but some are not.
There are few cognates between romanian and celtic languages also,like bou used to called the male of the cow which is identical to the celtic word for cow.
There is also R-L21 in Romania ,they found R-L21 at current romanian president as Y DNA.
There are arheological evidences linked with celts in Romania also,in Balkans also.