The W3C is the Internet governing body and its web guidelines can be found on its website:

http://www.w3.org/TR/WAI-WEBCONTENT/full-checklist.html

According to WebCredible (http://www.webcredible.co.uk/) it is widely believed that if a case around accessibility of websites makes it to court the W3C accessibility guidelines will be used to assess a website's accessibility and decide the outcome of the case.  It also points out that the Disability Rights Commission (DRC) launched a formal investigation into 1000 websites, of which over 80% were next to impossible for disabled people to use.  The DRC warns that organisations will face legal action under the DDA and the threat of unlimited compensation payments if they fail to make websites accessible for people with disabilities.

For more information go to:

http://www.drc-gb.org/library/website_accessibility_guidance/formal_investigation_report_w.aspx

http://www.drc-gb.org/library/website_accessibility_guidance.aspx

Other useful information on accessible websites can be obrained from the RNIB at the following webpage:

http://www.rnib.org.uk/xpedio/groups/public/documents/publicwebsite/public_accessiblewebsites.hcsp