Many retail web sites may be breaking the law by failing to be accessible to disabled users, despite the efforts of pressure groups to encourage improvements. According to a survey by charity AbilityNet, some of the UK's leading supermarkets are among the worst offenders.

AbilityNet tested supermarket web sites to find out how easily they could be used and accessed by disabled internet users - those suffering from vision impairment, dyslexia, or a physical disability that makes it difficult to use a mouse.

The organisation said that Sainsbury's, Asda, Somerfield and Morrisons failed to provide even the basic levels of accessibility for disabled users - though the supermarkets denied that they ignored the needs of disabled customers.

Morrisons said it was reviewing the content of its web site, and intended to launch a new integrated site in the near future that will be compliant with the Disability Discrimination Act (DDA). Sainsbury's said that it is addressing accessibility issues and is working to improve its service for all disabled customers later this year.

Somerfield released a statement: "Each Somerfield site complies with the World Wide Web Consortium's Web Accessibility Initiative A standard. We also worked with the RNIB and [have] achieved the organisation's 'See It Right Accessibility' standard."

AbilityNet said that of the sites it tested, only Tesco's alternative site for disabled users - at the first web address below - was easily accessible. "The Tesco site is also popular with the non-disabled because they find it easier to use," commented a spokeswoman for AbilityNet.

Robin Christopherson, AbilityNet's web consultancy manager, pointed out that companies with web sites that do not support access by disabled people could fall foul of the law.

Companies were given a five-year grace period by the Disability Rights Commission (DRC) to comply with the parts of the DDA that apply to the internet, which came into force in 1999.

"Some individuals have already won civil cases backed by specific charities for the disabled," said Christopherson. "These have been quietly settled out of court. But the DRC publicly served notice in April that it would also take legal action if necessary."