If you are responsible for marketing communications on your own or other websites then I recommend that you have a look at these links:

"Landmark agreement extends ASA's digital remit" - http://www.cap.org.uk/Media-Centre/2010/Extending-the-Digital-remit-of-the-CAP-Code.aspx

CAP Code (that will also apply to online advertising effective 1 March 2010) - http://www.cap.org.uk/The-Codes/CAP-Code.aspx