With hindsight many people will not know much about the L21 aka S145 Y-DNA Haplogroup so here is a very brief explanation.
R1bAround 15,000 years ago a man was born in Middle-East/West Asia region who was the first person to have the Y-DNA mutation referred to as the M343 SNP. He passed this mutation in his DNA to his sons, and they in turn to all of their direct male descendants. Any male now carrying this M343 SNP mutation is a descendant of this Middle-Eastern/West-Asian man and is said to belong to the R1b Haplogroup.
As time has passed by R1b men have had SNP mutations of their own thus forming multi-layered sub-groups of the R1b Haplogroup creating what is known as the R1b Phylogenetic Tree. A high level diagram of this can be found here with the original old M343 SNP mutation 3rd from top and progressively more recent SNP mutations as you follow the tree's branches down:-
http://xa.yimg.com/kq/groups/83659368/homepage/name/993461?type=snHigh level SNPs are typically found around the mediterranean, e.g., V88 is found mostly in North Africa, and it is not until you get down to the M269 SNP that you find a strong European connection. M269 is estimated to have first existed 10,000 yrs ago and is thought to have formed in the Balkans before spreading north-west, perhaps up the River Danube and round the Mediteranean shore (rivers and coasts are easily navigable unlike mountains and forests), into Europe some time after the last Ice Age.
Men carrying the M269 SNP have since spread throughout Western Europe, becoming the dominant population west of the River Rhine, and can be split into 3 main Western European groups:-
S21 or U106 - M269 men who also have a newer SNP mutation first known as S21 but also known as U106
S116 or P312 - M269 men who also have a newer SNP mutation known as P312
M269 - M269 men without either of the newer S21/U106 or S116/P312 mutations
As M269 has been in W. Europe longer than either of S21/U106 or S116/P312 it has spread to a slightly wider area than the other 2 groups. The areas where the 3 groups are concentrated can be summarised as:-
M269 - throughout all W Europe
S21/U106 - skewed to the north of Europe (N Germany, Denmark, Holland, Britain, etc)
S116/P312 - skewed to the south and west (Germany, France, Spain, Britain, etc)
and S116/P312 can be broken down further into sub-groups including:-
S28/U152 - concentrated in SW Europe
L21/S145 - concentrated in NW Europe from the German/French border up the Rhine, through Holland, Belgium and N.France and into the British Isles
S116/P312 - throughout all W Europe
A diagram attempting to show the overlap of these main sub-groups of European R1b can be seen here (note that the area where there is maximum overlap of these groups is France):-
http://img188.imageshack.us/img188/1994/r1b1b2confluence.gif