The Hong Kong (British Nationality) Order 1986
Article 4
Right to acquire new status of British National (Overseas)
4.—(1) On and after 1st July 1987 there shall be a new form of British nationality the holders of which shall be known as British Nationals (Overseas).
(2) Any person who is a British Dependent Territories citizen by virtue (wholly or partly) of his having a connection with Hong Kong and who, but for his having a connection with Hong Kong, would not be such a citizen shall be entitled, before 1st July 1997 (or before the end of 1997 if born in that year before that date), to be registered as a British National (Overseas) and to hold or be included in a passport appropriate to that status.
(3) Any person who, having become a British National (Overseas) by virtue of paragraph (2) above, ceases at any time before 1st July 1997 to be a British Dependent Territories citizen shall at the same time cease to be a British National (Overseas).