As long as it doesn't prove I'm part German!
Not a bad concept, but with mass migrations due to poverty, famine, illness etc, not to mention invasion by Belgians [yeah, who'd have ever thought that eh?] Romans, Norsemen etc etc, there cannot be a lot of pure blood [for want of a better term] left in this country.
Or are they able to look at my DNA and say "Right, there's 11% Irish, 32% Anglo Saxon, 46% Dutch and 11% Bull Mastiff" ?