:The definition of 'Foreign-born' should be based on that used by the the Office for National Statistics see cite here 
 "Country of birth cannot 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.