[danans]

10% of the average Briton's ancestry (for those without recently migrated ancestors) is attributable to West European Mesolithic hunter gathers. That's a pretty significant chunk, suggesting both migration and mixture happened, and not diffusion or replacement.

From https://www.nhm.ac.uk/our-science/our-work/origins-evolution...

"When we look at genetic variation in modern British people today, we find that – for those who do not have a recent history of migration – around 10% of their ancestry can be attributed to the ancient European population to which Cheddar Man belonged. This group is referred to as the western European Mesolithic hunter-gatherers. However, this ancestry does not relate specifically to Cheddar Man or the Mesolithic population of Britain. Well after Cheddar Man’s death, two large-scale prehistoric migrations into Britain produced significant population turnovers13. Both of these migrations into Britain represented westward extensions of population movements across Europe10-12. In both cases, these migrating populations intermixed with local people who carried western European Mesolithic hunter-gatherer ancestry, as they moved across Europe. When these populations arrived in Britain they already had some hunter-gatherer ancestry derived from this mixing with local populations. Therefore the majority of western European Mesolithic hunter-gatherers ancestry that we see in modern British people probably originates from populations who lived all over Europe during the Mesolithic, which was carried into Britain by these later migrations."