Well over half of government and council websites contain coding errors and break usability guidelines for the disabled.
The University of Southampton said 60% of UK government websites contained HTML errors and a similar number did not comply with guidelines aimed at improving web access for the disabled.
A major problem that web developers face is that a large number of authoring tools do not generate compliant HTML code, making it difficult to edit the coding.
The university said that even if a website looked fine to most users, and was free of errors, that did not mean the site would work with all browsers, and that it would be accessible to visually impaired people.
The university said web developers should follow guidelines to make sure websites could be accessed by any browser and on any sized screen.
The Disability Rights Commission (DRC) recently issued guidance for web developers to tackle the wider problem of inaccessible websites.
The DRC said 81% of British websites were inaccessible to disabled people, so the government sites are not at the bottom of the scale.
The guidance document, Publicly Available Specification (PAS) 78, has been developed by the British Standards Institution (BSI) and is sponsored by the DRC.
The PAS 78 guide is applicable to all organisations and is intended for use by those responsible for commissioning or maintaining public-facing websites and web-based services.
The document covers six key areas: the accessible website process, from commissioning to building a site; accessibility policies; what web accessibility guidelines mean; involvement of disabled people; compliance checking; and additional useful accessibility provisions.
Since 1999, website owners have had a legal duty under the Disability Discrimination Act (DDA) to ensure that services provided via the web are accessible to disabled people.