s 5 Duty to show British flag.
(1) Subject to subsection (2) below, a British ship, other than a fishing vessel, shall hoist the red ensign or other proper national colours— (a) on a signal being made to the ship by one of Her Majesty’s ships (including any ship under the command of a commissioned naval officer); and (b) on entering or leaving any foreign port; and (c) in the case of ships of 50 or more tons gross tonnage, on entering or leaving any British port. (2) Subsection (1)(c) above does not apply to a small ship (as defined in section 1(2)) registered under Part II.