The definitions used in the legislation which covers registration of disabled people are as follows (You may find some of the language used distasteful):
From the National Assistance Act 1948. Registration applies to people who are:
"18 or over who are blind, deaf or without speech, or who suffer from Mental Disorder of any description and other persons aged 18 or over who are substantially and permanently handicapped by illness, injury or congenital deformity or other such disabilities as may be prescribed by the minister."
From the Disabilities Discrimination Act 1995 which has taken the place of the Disabled Persons (Employment) Act 1944. The new act defines a disabled person as someone who has:
"a physical or mental impairment which has a substantial and long term adverse effect on his or her ability to carry out normal day-to-day activities."
You may also wish to become aware of the Chronically Sick and Disabled Persons Act 1970 which:
"was passed to ensure that local authorities provided the services to disabled people that allow them to live independently. The range of services include equipment and home adaptations needed to make the home safe or convenient or the disabled person. this can include ramps, flashing light systems, telephone equipment and services such as providing transport or support for educational or recreational services. Your local authority is obliged to inform you of other services available to you that are provided by the Council or other bodies."
Taken with permission from the Royal National Institute for Deaf People leaflet - "Your Rights to Services From Your Local Authority Under the Chronically Sick And Disabled Persons Act 1970"
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