Domesday, 4066 (Brace et al, 2018)

Even though population replacement should be expected at the start of the British Neolithic, the degree to which it appears to have occurred is stunning.  The numbers are roughly close to the ~93% figure that Harvard estimated in the Early Bronze Age (once you exclude the possibility of full-blooded Anatolians parachuting into the Isles).  In any case, take that percentage of surviving British HG's and then factor its surviving portion into the EBA.  It's not a lot, even in the extremities of the Isles.  In Wales, it's probably zero.  Stunning.

The notion of spear-chuckers snapping spears over their legs and adopting the farming lifestyle didn't happen in Britain.  It looks like they were just out-produced, out-bred and over-run.

Farmer baby machine aside, they make a comment that is difficult to escape...

"In summary, our results indicate that the progression of the Neolithic in Britain was unusual when compared to other previously studied European regions. Rather than reflecting the slow admixture processes that occurred between ANFs and local hunter-gatherer groups in areas of continental Europe, we infer a British Neolithic proceeding with little introgression from resident foragers – either during initial colonization phase, or throughout the Neolithic. This may reflect the fact that farming arrived in Britain a couple of thousand years later than it did in Europe. The farming population who arrived in Britain may have mastered more of the technologies needed to thrive in northern and western Europe than the farmers who had first expanded into these areas. A large-scale seaborne movement of established Neolithic groups leading to the rapid establishment of the first agrarian and pastoral economies across Britain, provides a plausible scenario for the scale of genetic and cultural change in Britain."

I'm eager to see if it's possible to tease out some structure to the farmer groups in Britain based on geography and cultural context.  It seems that could be the case.

Population Replacement in Early Neolithic Britain

Selina Brace1*, Yoan Diekmann2*, Thomas J. Booth1*, Zuzana Faltyskova2, Nadin Rohland3,
Swapan Mallick3,4,5, Matthew Ferry3,4,, Megan Michel3,4,, Jonas Oppenheimer3,4, Nasreen
Broomandkhoshbacht3,4, Kristin Stewardson3,4, Susan Walsh6, Manfred Kayser7, Rick
Schulting8, Oliver E. Craig9, Alison Sheridan10, Mike Parker Pearson11, Chris Stringer1, David
Reich3,4,5#, Mark G. Thomas2#, Ian Barnes1#
bioRxiv preprint first posted online Feb. 18, 2018; doi: http://dx.doi.org/10.1101/267443.
[Link]

Abstract

The roles of migration, admixture and acculturation in the European transition to farming have been debated for over 100 years. Genome-wide ancient DNA studies indicate predominantly Anatolian ancestry for continental Neolithic farmers, but also variable admixture with local Mesolithic hunter-gatherers. Neolithic cultures first appear in Britain c. 6000 years ago (kBP), a millennium after they appear in adjacent areas of northwestern continental Europe. However, the pattern and process of the British Neolithic transition remains unclear. We assembled genome-wide data from six Mesolithic and 67 Neolithic individuals found in Britain, dating from 10.5-4.5 kBP, a dataset that includes 22 newly reported individuals and the first genomic data from British Mesolithic hunter-gatherers. Our analyses reveals persistent genetic affinities between Mesolithic British and Western European hunter-gatherers over a period spanning Britain's separation from continental Europe. We find overwhelming support for agriculture being introduced by incoming continental farmers, with small and geographically structured levels of additional hunter-gatherer introgression. We find genetic affinity between British and Iberian Neolithic populations indicating that British Neolithic people derived much of their ancestry from Anatolian farmers who originally followed the Mediterranean route of dispersal and likely entered Britain from northwestern mainland Europe.