Many UK supermarkets’ web sites fail to meet minimum accessibility standards and may contravene the Disability Discrimination Act, according to new research by computing and disability specialist AbilityNet.

AbilityNet looked again at the top five food retailer's web sites, after an earlier review in 2004, to see what progress had been made, and found only Tesco exceeded minimum standards, gaining four out of five stars.

Morrisons achieved a three-star rating but is an information-only site, while Sainsbury's, Asda and Somerfield all failed to improve on their ratings in 2004.

"Two years on we hoped to see more progress," said AbilityNet's senior consultant Jon Gooday. "There is an awareness of the key challenges and the business case, it's just translating that into action [that is lacking]."

Common criticisms included small text, hard-coded colours, so users cannot change the site's background colour, and too much Flash, which sometimes interferes with screen-reading technology, said Gooday.

"Often there is almost too much information on the homepage, which a lot of people struggle with," said Gooday. "Tesco gives users the choice of using the normal site or the accessible version which is cleaner [with less] pictures and graphics – that's the trend in terms of where sites should be going."

In recent years, AbilityNet has surveyed many leaders in e-commerce, including airlines, banks and telecoms providers, many of which have failed accessibility tests.