Up to one in 10 web sites presents accessibility problems to some types of web browser, according to a report released in June by web site testing specialist SciVisum.

SciVisum looked at 100 leading UK consumer web sites and found that 10 percent created access difficulties for certain types of browser.

Three percent would only allow access to Internet Explorer users, while a further seven percent included code that could only be viewed through Explorer. Some sites, including the Odeon cinema web site, which was singled out for being inaccessible, could be viewed on other browsers, but only in text format.

Sites that used non-standard web coding, often viewable only to Explorer users, included British American Tobacco and the insurance arm of Lloyds TSB.

To ensure that web sites are visible across all browsers SciVisum recommended they should be developed to be compliant with widely accepted standards, and only then should they be tailored for individual browsers.

Deri Jones, chief executive at SciVisum, commented, "Start with a foundation in standards by developing for Firefox, then tweak it for Internet Explorer."

Jones said that the growing use of standards-compliant browsers, such as Mozilla's Firefox, meant that web developers should develop code around the W3C's Cascading Style Sheets 2 (CSS2) web standard. He added that non-standard code could limit a web sites' audience and alienate users of minority web browsers. "There are a number of key sites out there that have not caught on," he said. "Companies who value their brand need to address browser issues immediately."

The use of alternatives to Explorer is growing. Use of Firefox has grown and now accounts for some seven percent of browsers - which has prompted Microsoft to announce it will release a new version of Explorer.

Although Microsoft has not yet detailed the changes coming with version 7.0 of Explorer, Jones predicted it might adhere more closely to common web standards. "That could be a real challenge for firms," he added. "If version 7.0 is significantly different from version 6.0 it may not work with their sites."