The government web site www.direct.gov.uk states... 

You are eligible disabled if you:

• are blind or partially sighted
• are profoundly or severely deaf
• are without speech
• have a disability, or have suffered an injury, which has a substantial and long-term adverse effect on your ability to walk
• do not have arms or have long-term loss of the use of both arms
• have a learning disability - a state of arrested or incomplete development of mind which includes significant impairment of intelligence and social functioning, or
• would, if you applied for a licence to drive a motor vehicle under Part III of the Road Traffic Act 1988, have your application refused under section 92 of the Act (physical fitness) on grounds other than persistent misuse of drugs or alcohol