"In this article "leave" means - (a) leave to enter the United Kingdom (including leave to enter conferred by means of an entry clearance under article 2); and (b) leave to remain in the United Kingdom."
"For the purposes of paragraphs 2 and 2A of Schedule 2 to the Act (examination by immigration officers, and medical examination), leave to remain which remains in force under this article shall be treated, upon the holder's arrival in the United Kingdom, as leave to enter which has been granted to the holder before his arrival."
"2A(1) This paragraph applies to a person who has arrived in the United Kingdom with leave to enter which is in force but which was given to him before his arrival. (2) He may be examined by an immigration officer for the purpose of establishing -- (a) whether there has been such a change in the circumstances of his case, since that leave was given, that it should be cancelled;"