So with british law, the intent of the law is as important as the written texts. Listen to the debates which can and are used by judges from the commons and the lords to decide upon intent. It's not for tiny forums, but I'm also not a lawyer. Significant most likely relates to not just user count, but also other reporting from other media, it's significance of significant users, anonymity, and ability to break bigger stories. Try codifying any of that (and more!) in a law