Chapter 38, Sections 145 & 146:
Mandatory concessions Outside London

http://www.opsi.gov.uk/acts/acts2000/00038--w.htm

145. - (1) Any person to whom a current statutory travel concession permit has been issued by a travel concession authority and who travels on an eligible service on a journey-
 

(a) between places in the authority's area, and

(b) beginning at a relevant time, is entitled, on production of the permit, to be provided with a half-price travel concession by the operator of the service.
 

(2) A travel concession authority must, on an application made to it by any person who appears to the authority to be an elderly or disabled person residing in its area, issue to the person free of charge a permit, in such form and for such period as the authority considers appropriate, indicating that he is entitled to the concession specified in subsection (1).

Section 146:
Mandatory concessions supplementary

146. In this Part-

"disabled person" means a person who-
 

(a) is blind or partially sighted,

(b) is profoundly or severely deaf,

(c) is without speech,

(d) has a disability, or has suffered an injury, which has a substantial and long-term adverse effect on his ability to walk,

(e) does not have arms or has long-term loss of the use of both arms,

(f) has a learning disability, that is, a state of arrested or incomplete development of mind which includes significant impairment of intelligence and social functioning, or

(g) would, if he applied for the grant of a licence to drive a motor vehicle under Part III of the Road Traffic Act 1988, have his application refused pursuant to section 92 of that Act (physical fitness) otherwise than on the ground of persistent misuse of drugs or alcohol,

Department for Transport
Guidance to local authorities on eligibility for disabled people
Published 31 May 2001, modified 22 November 2005 to reflect the change in statutory minimum entitlement

http://www.dft.gov.uk/pgr/regional/buses/concessionary/local/guidancetolocalauthoritieson3561

"(c) is without speech"

26. Included within this category are people who are unable to communicate orally in any language. Those people will be:

• unable to make clear basic oral requests e.g. to ask for a particular destination or fare;
  
  
• unable to ask specific questions to clarify instructions e.g. "Does this bus go to the High Street?"

27. This category would not, in the Department's opinion, cover people who are able to communicate orally but whose speech may be slow or difficult to understand because, for example, of a severe stammer.

28. In considering an application on these grounds the local authority may reasonably seek medical evidence to support the application in appropriate cases.