He may be made a knight, sure enough ,and a woman can be made a dame, but the honour is styled 'honorary' and the bearer is not permitted to be styled Sir.. or Dame.. They are however entitled to have the letters K.B.E. or D.B.E. after their names (for Knight Commander or Dame Commander of the Order of the British Empire). The honour is the highest honour that The Queen bestows on anyone who is not a British citizen.There are people who have been so honoured who were formerly British citizens as adults. e.g the broadcaster Alistair Cook KBE and numbers who were born British citizens but left as children when their parents emigrated e.g. Bob Hope KBE . Both groups are entitled to resume citizenship and be Sir or Dame, of course, but Bob Hope has said that he only left because he had discovered that he couldn't become King, so it's unlikely in his case ! The reason for the rule seems to be simply to show that the person holds it as an honour and with no other qualification , obligation or duty (and distinguishes them from the time-servers, sycophants, bureaucrats and incompetent heads of large organisations who make up such a large proportion of the rest! ).