From the website..
Welcome to the Cinema Exhibitors' Association Card Website. This is a national card that can be used to verify that the holder is entitled to one free ticket for a person accompanying them to the cinema.
To apply for the card, you will need to meet one or more of the following criteria:
a) Be in receipt of the disability living allowance or attendance allowance.
b) Be a registered blind person.
c) Be a holder of a disabled person's rail card.
The card is valid for 3 years from the date of issue.
Application forms are available from cinemas across the UK supporting this card. Alternatively, Download a form to print out and fill in.
A processing fee of five pounds is chargeable per card. This is to be sent along with the completed application.
There is a list of participating Cinemas on their website!