Where a person arrives at a place in the United Kingdom as a member of the crew of a ship or aircraft under an engagement requiring him to leave on that ship as a member of the crew, or to leave within seven days on that or another aircraft as a member of its crew, then unless either—
(a) there is in force a deportation order made against him; or
(b) he has at any time been refused leave to enter the United Kingdom and has not since then been given leave to enter or remain in the United Kingdom; or
(c) an immigration officer requires him to submit to examination in accordance with Schedule 2 to this Act; ...
(d) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
he may without leave enter the United Kingdom at that place and remain until the departure of the ship or aircraft on which he is required by his engagement to leave.
Subsection (1) does not apply in relation to a member of the crew of a ship who is an offshore worker within the meaning of section 11A.
Subject to subsection (3A) below, the provisions of this Act relating to those who are not British citizens shall not apply to any person so long as he is a member of a mission (within the meaning of the Diplomatic Privileges Act 1964), a person who is a member of the family and forms part of the household of such a member, or a person otherwise entitled to the like immunity from jurisdiction as is conferred by that Act on a diplomatic agent.
For the purposes of subsection (3), a member of a mission other than a diplomatic agent (as defined by the 1964 Act) is not to count as a member of a mission unless—
(a) he was resident outside the United Kingdom, and was not in the United Kingdom, when he was offered a post as such a member; and
(b) he has not ceased to be such a member after having taken up the post.
The provisions of this Act relating to those who are not British citizens, other than the provisions relating to deportation, shall also not apply to any person so long as either—
(a) he is subject, as a member of the home forces, to service law; or
(b) being a member of a Commonwealth force or of a force raised under the law of any . . . colony, protectorate or protected state, is undergoing or about to undergo training in the United Kingdom with any body, contingent or detachment of the home forces; or
(c) he is serving or posted for service in the United Kingdom as a member of a visiting force or of any force raised as aforesaid or as a member of an international headquarters or defence organisation designated for the time being by an Order in Council under section 1 of the International Headquarters and Defence Organisations Act 1964.
In this section "the home forces" means any of Her Majesty's forces other than a Commonwealth force or a force raised under the law of any associated state, colony, protectorate or protected state; "Commonwealth force" means a force of any country to which provisions of the Visiting Forces Act 1952 apply without an Order in Council under section 1 of the Act; and "visiting force" means a body, contingent or detachment of the forces of a country to which any of those provisions apply, being a body, contingent or detachment for the time being present in the United Kingdom on the invitation of Her Majesty's Government in the United Kingdom.