2(1)A person shall be disregarded for the purposes of discount on a particular day if—E+W+S
(a)on the day he is severely mentally impaired;
(b)as regards any period which includes the day he is stated in a certificate of a registered medical practitioner to have been or to be likely to be severely mentally impaired; and
(c)as regards the day he fulfils such conditions as may be prescribed by order made by the Secretary of State.
(2)For the purposes of this paragraph a person is severely mentally impaired if he has a severe impairment of intelligence and social functioning (however caused) which appears to be permanent.
(3)The Secretary of State may by order substitute another definition for the definition in sub-paragraph (2) above as for the time being effective for the purposes of this paragraph.