Hmmmm.... I suspect that DNA will not be the panacea that some are expecting it to be. Recently I have been doing some research on my father's first wife, and have found that she was a distant cousin of his second wife (my mother !). So, my half-brother is not only my half-brother, but he's also a very distant cousin. I should add that neither woman knew each other, and they were born in totally different counties, but one family line originated in Norfolk, and the other in Suffolk. DNA is really only useful for proving whether a man is the father of a child, or for locating an area in the world where a family came from, but it's not really going to help you trace your roots back to the middle ages or beyond.
If you do simple maths, and realise that every time you go back a generation you double the number of g.g.g...... grandparents responsible for you being here, it soon becomes apparent that you only have to go back about 10 generations for the number of people needed to produce you becomes very large. Go back about 15 to 20 generations, and the number of people exceeds the population of the UK at that time, so if your ancestors were "pure British", then you are DNA-related to everyone else in the UK with a "pure British" blood line (whatever that is

).