Using a bit of math, it's a fairly easy task to establish that almost everyone with British Isles or European ancestry is most likely related, probably with ancestors who lived within the last 1,000 to 2,000 years. Why?

Well, if we estimate 25 years between successive generations, then go back a mere 1,000 years of our circa 100,000 to 150,000 years of existence as modern humans, we can establish that each of us has had 1,099,511,627,776 (that's one trillion, ninety-nine billion, five hundred and eleven million, six hundred and twenty-seven thousand, seven hundred and seventy-six great (repeated 38 times) grandparents... and that's just in the last millennium! I'm quite sure that there weren't that many individuals on the planet 1,000 years ago. The only way I believe we can account for that huge number is if a good portion of that count can be reduced through "relatedness".

If we were to go back about 1,450 years, here's the "approximate" number of great-grandparents you'd have:

Two hundred and eighty-eight quadrillion, two hundred and thirty trillion, three hundred and seventy-six billion, one hundred and fifty-one million, seven hundred and twelve thousand

Here's the table I created using Microsoft Excel (yes, it's a bit "nerdy", but I hope you get the point...):