Companies such as Google, Facebook and Twitter, which rely on the public for their content but take no responsibility for what is uploaded, have long claimed to be mere facilitators.
The online platforms could potentially face claims for millions of dollars in damages if defamatory comments are not swiftly deleted after a complaint has been received.
Lord Justice Richards said: “Even if Google should properly be seen as a facilitator, the mere provider of a gigantic notice board on which others published defamatory material, in my judgment it must also at least be arguable that at some point after notification became liable for continued publication of the material complained of.”
The case brought to the Court of Appeal was by Payamin Tamiz, a former Conservative candidate in the UK, who complained of smears on Google’s Blogger.com site.
Tamiz said he complained to Google about the posts in early July 2011, but they were not removed until August 14, 2011.