Many UK companies are being urged to update information on their web sites and in email footers or risk a fine after amendments to the Companies Act passed into law last week increased the amount of information that has to be disclosed in electronic documents.

Under the new rules, every company is required to list its company registration number, place of registration and registered office address on its web site, order forms and other electronic business letters.

Legal experts said that, while hard copy business letters have previously had to include this information, there had been confusion over whether electronic documents were also affected. However, the latest amendments confirm electronic documents do qualify as business letters and, as a result, companies are being advised to automatically include the information on all emails and other electronic documents to remove the hassle of users having to decide whether communications constitute a "business letter" or not.

Paul Gershlick, IT and commercial solicitor at law firm Matthew Arnold & Baldwin, said many companies are likely to have been caught out by the change and are now at risks of fines.

"The amendments were put before Parliament just before Christmas and passed into law on the first of January, when many people were still on holiday," he said. "Changes to websites need to be made as soon as possible as both the firm and its directors are at risk of fines."

He added that, as "a rule of thumb", IT chiefs should now ensure that all the company information included on hard copy business letters is automatically included on emails and added to web sites.