I am not sure how Ancestry get their results. Mine is 49% British and 49% German. This means one of my parents must have been British and the other German. I moved to the UK 15 years ago. But both my parents where German as where my 4 grandparents and my 8 great-grandparents. It seems to me they have rolled the dice and assumed that if you send a sample from the UK you must have British ancestry. No science behind it at all. I could have gone to the oracle at the fun fair.
The spit is for one of the home genetic-testing kits I’m sampling. A growing number of these kits (brands such as 23andMe, DNAFit, Thriva, MyHeritage DNA, and Orig3n) promise to unlock the mystery of your genomes, variously explaining everything from ancestry, residual Neanderthal variants, “bioinformatics” for fitness, weight loss and skincare, to more random genetic predispositions, denoting, say, the dimensions of your earlobes or the consistency of your earwax.