what you have got to understand is where this myth of the noble celt s driven out by the blood thirsty anglosaxons has come from.
Henry Tudor, the Welsh conqueror king, invented it.
He needed as many props to his claim to the throne as possible
His idea was to claim that the celts lived all over the UK and owned the land by right, until the lawless anglo saxons took over.
This story stood from the 1600 to the late twentieth century
Proper REAL DNA analysis, and other forms of scientific archeology show a completely different story
The population of the british isles/ireland are basically descendent of the ancient brits. There is influence from celtic invasions in the west, but they did not diplace the ancient brits, and anglosaxons from the east, who also did not displace them
Roman influences can be found, but genetically indistinguishable from "anglo saxons" as they were basically the same soldiers fighting for different armies. Same individuals.
YOU might be interested to know large amounts of DNA from Africa also brough over by the Romans, particularly to North England and Scotland
There was Viking influences too, but almost no Norman influence, for the same reason. The "Norman" army and the "Viking" army were largely the same men fighting for different armies. Same individuals even, not just same families
Of course not one iota of ay of this shows up in these commercial companies, because all of this DNA, including the African DNA, is found in the UK, so in their spread sheet, likely to be classed as UK most of the time.
But of course, any Brit is largely British, but also a mixture of all these other influences, African, Norwegian, Germanic, Mediterranean, middle eastern. Asian too, it would only take one Asian Roman soldier on the scottish border 1800 years ago for every single Brit to have a tiny fraction of his DNA now
Go back to Edward first, every Brit is related to every other Brit, (and descended from Edward first)
(By Brit I am talking about the indigenous population - obviously)
But if one of these companies tells you about a percent of African DNA, its just most likely picked up on what is normally counted as British DNA, but does originate in Africa,