Receipt of a qualifying benefit is also required.
Local Government Finance Act 1992
2.—(1) A person shall be disregarded for the purposes of discount on a particular day if—
(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
http://www.legislation.gov.uk/ukpga/1992/14/schedule/1
Council Tax Discounts order 1992 SI 1992 no 548
3.—(1)
The condition prescribed for the purposes of paragraph 2(1)(c) of Schedule 1 to the Act is that the person in question is entitled to one of the qualifying benefits listed in paragraph (2) below.
(2) The qualifying benefits for the purposes of paragraph (1) are—
(a) an invalidity pension under section 33, 40 or 41 of the Social Security Contributions and Benefits Act 1992<5>;
(b) an attendance allowance under section 64 of that Act;
(c) a severe disablement allowance under section 68 of that Act;
(d) the care component of a disability living allowance under section 71 of that Act, payable at the highest rate under section 72(4)(a) or at the middle rate under section 72(4)(b) of that Act;
(e) an increase in the rate of his disablement pension under section 104 of that Act (increase where constant attendance needed);
(f) a disability working allowance under section 129 of that Act for which the qualifying benefit is one falling within subsection (2)(a)(i) or (ii) of that section, or is a corresponding Northern Ireland benefit;
(g) an unemployability supplement under Part I of Schedule 7 to that Act;
(h) a constant attendance allowance under—
(i) article 14 of the Personal Injuries (Civilians) Scheme 1983<6>; or
(ii) article 14 of the Naval, Military and Air Forces etc. (Disablement and Death) Service Pensions Order 1983 (including that provision as applied, whether with or without modifications, by any other instrument);
(i) an unemployability allowance under—
(i) article 18(1) of the Personal Injuries (Civilians) Scheme 1983<7>, or
(ii) article 18(1) of the Naval, Military and Air Forces etc. (Disablement and Death) Service Pensions Order 1983 (including that provision as applied, whether with or without modifications, by any other instrument).
http://www.legislation.gov.uk/uksi/1992/548/article/3/made