According to internet company Nomensa, 75% of the FTSE 100 companies it tested did not meet the minimum requirements of the Disability Discriminations Act.
The main complaint was not letting users increase text size, which can exclude people with sight problems.
Other problems included a lack of text descriptions for pictures, text-heavy pages, and too much use of jargon.
Nomensa is a company that creates websites. It said its research found problems across all the major industries.
It did, however, single out some companies as being ahead of their peers, including Marks & Spencer, Sainsbury, Alliance & Leicester, Royal Sun & Alliance, Yell Group, Rentokil, and GlaxoSmithKline.
The best-performing were Daily Mail General Trust and Xstrata, which missed out on a double AA rating by one point. None of the websites tested achieved a double or triple A rating.
Nomensa said that it based its testing on "globally recognised Web Content Accessibility Guidelines".
Five most common flaws (Source: Nomensa):
Source: BBC News Website (http://news.bbc.co.uk)
Date: 27th April 2006