17Patients liable to be detained in hospital
(1)A person may, in pursuance of an application for admission under section 18(1) of this Act, be admitted to a hospital and there detained on the grounds that—
(a)he is suffering from mental disorder of a nature or degree which makes it appropriate for him to receive medical treatment in a hospital; and
(i)in the case where the mental disorder from which he suffers is a persistent one manifested only by abnormally aggressive or seriously irresponsible conduct, such treatment is likely to alleviate or prevent a deterioration of his condition; or
(ii)in the case where the mental disorder from which he suffers is a mental handicap, the handicap comprises mental impairment (where such treatment is likely to alleviate or prevent a deterioration of his condition) or severe mental impairment; and
(b)it is necessary for the health or safety of that person or for the protection of other persons that he should receive such treatment and it cannot be provided unless he is detained under this Part of this Act
(2)Nothing in this Act shall be construed as preventing a patient who requires treatment for mental disorder from being admitted to any hospital or nursing home for that treatment in pursuance of arrangements made in that behalf without any application, recommendation or order rendering him liable to be detained under this Act, or from remaining in any hospital in pursuance of such arrangements if he has ceased to be so liable to be detained.