The British Standards Institution has published guidance on making sure that your website is disability-friendly. Under the Disability Discrimination Act, it is unlawful for a service provider to discriminate against a disabled person by refusing to provide any service which it provides to members of the public and a service provider has to take reasonable steps to change a practice which makes it unreasonably difficult for disabled people to make use of its services.
If you want to have your website reviewed for usability by disabled people, the Usability Exchange offers such a service for a fee.

