Thanks, this has been very interesting to read.
"Warburton is an example where it is recognised that pretty much anyone with the surname can be traced back to a single village with the same name eventually."
In a similar vein, my maternal grandmother was a Stinchcombe and, likewise, pretty much everyone with that name can be traced back to the village with the same name which is half way between Gloucester and Bristol.
But I also have other family names that crop up all the time as well, Like Clutterbuck and Rodway. The Clutterbucks originally come from the village of Berkeley, about four miles away from Stinchcombe (although it is also said that the descent is from Dutch immigrants of that name, who were weavers, who settled in the area around Berkeley in the 1400s).
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"I can generally tell when a new match comes up whether they are British or American just from their name."
Again, that's really interesting to hear. The nearest I can get with that is when there are particular names in their family tree.
For example, overall out of 270 DNA matches that I have traced (for context, both of my parents have their DNA on Ancestry) the split by country was:
UK 60%
USA 16%
Canada 11%
Australia 6.5%
New Zealand 6.5%
However, where I mentioned Stinchcombe above, I've found that if anybody has that name in their tree then it is roughly a 50/50 chance that they are in the USA (even though only 16% of all matches I've traced are in the USA).
This goes back to some distant relations who left Gloucestershire in the 1600s for the sunny climes of Maryland and who later bred like rabbits (and also intermarried a lot as well).
Likewise, my dad had some relations who became Mormons and left Gloucestershire for Utah in the 1860s. Today, if there is anyone who comes up with a particular surname in their tree and/or lives in Utah then I know exactly how we are related.