The study of 50 disability websites, most of which are charity portals, found that 58 per cent did not sufficiently meet the web content compliance accessibility guidelines that are set by global standards body, the World Wide Web Consortium.
The results of Ethical Media's survey have prompted Keith Patton, its head of digital communications, to issue a stark warning to charities that they risk huge embarrassment.
"If large charities are considering taking large companies to court under the Disability Discrimination Act for having inaccessible websites, it is essential that they aren't undermined by poor accessibility compliance and sneering comments about their hypocrisy."
The guidelines provide three ratings. The survey found that 42 per cent had met the minimum requirements, but just 14 per cent had achieved the higher 'important' level of compliance and only 8 per cent had reached a 'desirable' level.
"This reveals the gap between the rhetoric and the reality of disability groups' communications activities," said Patton.
Two charities - the British Council for Disabled People, and Ability Net, which champions IT for people with disabilities - were commended for their sites.
Carrie Saintfreedman, press officer at Ability Net, said: "I'm not surprised by these figures because compliance rates are generally appalling. Most sites are built without any compliance consideration at all, and those websites already in existence are tricky to alter technically."
The Leonard Cheshire and RNIB sites were absent from the list of commendations.
The RNIB has pursued a number of civil claims with high-street firms, all of which are settling out of court.