The Public Health (Aircraft) Regulations 1979

27.  Where an aircraft is due to depart from an aerodrome for a destination outside the United Kingdom, the medical officer—

(a) may examine any person who proposes to embark thereon if he has reasonable grounds for believing him to be suffering from a disease subject to the International Health Regulations, and, if after examination the medical officer is of the opinion that he shows symptoms of such a disease, shall prohibit his embarkation and the time and place of this examination shall be arranged so as to take into account any other formalities and to avoid delay;

(b) shall prohibit any suspect from embarking thereon:

Provided that in the case of smallpox a person shall not be prohibited from, embarking if he satisfies the medical officer that he is sufficiently protected by vaccination or by a previous attack of smallpox;

(c) shall notify by the most expeditious means the commander and the health authority for the place to which the person is proceeding of any person embarking or proposing to continue his voyage thereon who, in the opinion of the medical officer, should be placed under surveillance;

(d) notwithstanding the provisions of sub-paragraph (b) of this regulation a person on an international voyage who on arrival was placed under surveillance may be allowed to continue his voyage. The medical officer shall notify by the most expeditious means the health authority for the place to which the person is proceeding that such a person should in the opinion of the medical officer, be placed under surveillance.