The Telegraph‘s “premium” offering is struggling. Online ABCs for December released this week show average daily unique visitors down 13.2% year on year. This paywall induced fall means the Telegraph has now slipped behind the re-vamped Sun site, despite heavy investment in targeting a popular audience. Things are so bad that the Telegraph has taken to advertising on MailOnline. Although almost certainly programmatic, ironic to see a huge Telegraph banner plastered across the front of the world’s most visited news website…