Any person (other than a person subject to guardianship) who—
(a)under section 30 or section 108 of the Mental Health Act (Northern Ireland) 1961 (which provide respectively for the retaking of patients absent without leave and for the retaking of patients escaping from custody) ; or
(b)under the said section 30 as applied by section 34 of the said Act of 1961 (which makes special provision as to persons sentenced to imprisonment);
may be taken into custody in Northern Ireland, may be taken into custody in, and returned to Northern Ireland from, Scotland by a mental health officer, by any constable or by any person authorised by or by virtue of the said Act of 1961 to take him into custody.