Sch 2 para 2
(1) An immigration officer may examine any persons within sub-paragraph (1A) arrived in the United Kingdom by ship or aircraft (including transit passengers, members of the crew and others not seeking to enter the United Kingdom) for the purpose of determining— (a) whether any of them is or is not a British citizen ; and (b) whether, if he is not, he may or may not enter the United Kingdom without leave; and (c) whether, if he may not— (i) he has been given leave which is still in force, (ii) he should be given leave and for what period or on what conditions (if any), or (iii) he should be refused leave ; and (d) whether, if he has been given leave which is still in force, his leave should be curtailed. (1A) The persons are— (a) any person who has arrived in the United Kingdom by ship or aircraft (including transit passengers, members of the crew and others not seeking to enter the United Kingdom); (b) any person who has arrived in United Kingdom waters by ship or aircraft who the immigration officer has reason to believe is an offshore worker. (1B) In sub-paragraph (1A), “ offshore worker ” and “ United Kingdom waters ” have the same meaning as in section 11A. (2) Any such person, if he is seeking to enter the United Kingdom, may be examined also by a medical inspector or by any qualified person carrying out a test or examination required by a medical inspector. (3) A person, on being examined under this paragraph by an immigration officer or medical inspector, may be required in writing by him to submit to further examination; but a requirement under this sub-paragraph shall not prevent a person who arrives as a transit passenger, or as a member of the crew of a ship or aircraft, or for the purpose of joining a ship or aircraft as a member of the crew, from leaving by his intended ship or aircraft.