28. Where the address of a person who is on the contractor's list of patients is no longer known to the Board, the Board must—
(a)give notice in writing to the contractor that it intends, at the end of the period of six months beginning with the date on which the notice was given, to remove the person from the contractor's list of patients; and
(b)at the end of the period referred to in sub-paragraph (a), remove the person from the contractor's list of patients unless, before the end of that period, the contractor satisfies the Board that the person is a patient to whom it is still responsible for providing essential services.