I can't find the original story, but I read at one point that if you go about 22 generations back (excluding recent immigrants) everybody in the UK is related to everybody else in the UK, so there are probably a whole lot more famous people in England who are related as closely as 16th cousins. The trick is tracing out the tree accurately, but that is much easier in the UK where church records recording births and deaths were kept much more rigorously than in the USA.