Without some Nazi style racial test it would be impossible to come to any form of conclusion, quite a high percentage of the UK population will have some Asian or African input and has said before it is likely that those with say a 25% or less none European input will class themselves as white British/English etc. This mix is nothing new .. somewhere I have the reprint of a journal of a journey through England & Wales written circa 1852 by George Webb Medley, George Webb Medley although considered by himself and others as English was in fact of 25% African decent. He endowed Oxford University with The George Webb Medley Scholarship.