All web sites that are owned by UK businesses need to comply with the Disability Discrimination Act - The DDA. The Disability Discrimination Act 1995 - was introduced with the intention of comprehensively tackling the discrimination which many disabled people face. The part of the DDA that states web sites must be made accessible came into force on 1 October 1999 and the Code of Practice for this section of the Act was published on 27 May 2002. If you are a business with an online presence it is important that you are aware of this act.
Further information:

Royal National Institute of the Blind

Web Accessibility and UK Law