The definition of Foreign born should be based on that used by the the Office for National Statistics see cite here Country of birth can not change over time unlike nationality and so those born outside the UK represent a stable definition of a migrant It is a measure of foreign born people but includes some people who were UK citizens at birth even though born abroad for example to parents working overseas in the Armed Forces Additionally many usual residents of England and Wales born outside the UK will have subsequently become UK citizens It might be worth seeing whether the article would be improved by making this clearer