The map below is from Donnelly (2015). They tried to find people who lived near to where all their grandparents had lived, and found 2,039 individuals. Genes of Angles and Saxons dominate in the south and east of England. However, more than half of this gene pool derives from pre-existing inhabitants of the region.
Loanwords from Welsh to English are fewer than 10: bard, corgi, crag, coracle, penguin, dad, flummery.
Why so few? There may be more subtle persistence of the Welsh sound written “th” in English; there is also a hint in the “ll” in Icelandic. Welsh syntax order is V-S-O and it has initial phonetic mutations.
The map below shows Celtic kingdoms after the Romans but before the Anglo-Saxons.
The “old north” (yr hen ogledd) included Lancashire, Cumbria and Strathclyde. The map below shows Welsh place names from the kingdom of Rheged, which was absorbed into Northumbria in 730 CE and the kingdom of Strathclyde which continued till about 1100.
There was a migration from Ireland to what is now south-west Scotland and became the kingdom of Dal Riata. They chose the Roman names Scoti for themselves and Alba (‘white’) for the country.
Loanwords from Scots Gaelic into general English are:
bard bog bothy caber cairn capercaillie ceilidh clan claymore corrie crag galore gillie glen kyle loch mackintosh pet pibroch pillion plaid ptarmigan Sassenach shindig slogan sporran spunk Strontium tacksman trousers whisky
The next map shows how the Celtic League views the ethnic groups of the British Isles. Dark green shows a high density of speakers of the Celtic language.
The modern region of Scotland includes people derived from three groups of Celts: the Gaelic speakers of Dal Riata; the Welsh speakers of Strathclyde; the p-Celtic speakers of Pictland. South-east Scotland is mainly people by Anglo-Saxons who once made up the northern part of the kingdom of Northumbria. There are also Scandinavian genes, including the inhabitants of Orkney and Shetland and traces in the descendants of Robert de Brus and his Norman followers. The Scots dialect of English takes its vowels from Northumbrian.