A European judgment about an Estonian news site should worry all websites allowing users to comment below online articles.

Until now, prompt removal upon complaint has provided a defence against libel actions. This ruling by the European Court of Human Rights suggests websites need to police their comments and anticipate when a story will attract defamatory posts.

This will place a huge burden on news sites, which will need to review their moderation if the judgment is not challenged and rejected in the ECHR's grand chamber.

The case concerned Estonia's Delfi news website and a story about a ferry company which had changed its routes, damaging ice roads, thus preventing people using them. The ice roads are a cheaper alternative to ferries and a number of people posted abusive and defamatory comments about the company's main shareholder on the site.

The shareholder, named "L" in the judgement, complained about the postings in writing, but did not make use of the site's automated complaint flagging system.

Delfi accepted the comments were defamatory and removed them as soon as they received that complaint, but by that time they had been live for six weeks. Delfi was successfully sued in the Estonian courts, prompting its appeal to the ECHR.

We have always relied on rulings such as Godfrey v Demon Internet and Kaschke v Gray & Hilton which say removal on notice provides a defence to those who provide such online comment facilities.

A section in the judgment which should send a shiver of fear down any website operator's spine is: "The court considers that the applicant company, by publishing the article in question, could have realised that it might cause negative reactions against the shipping company and its managers and that, considering the general reputation of comments on the Delfi news portal, there was a higher-than-average risk that the negative comments could go beyond the boundaries of acceptable criticism and reach the level of gratuitous insult or hate speech.

"It also appears that the number of comments posted on the article in question was above average and indicated a great deal of interest in the matter among the readers and those who posted their comments. Thus, the court concludes that the applicant company was expected to exercise a degree of caution in the circumstances of the present case in order to avoid being held liable for an infringement of other persons' reputations."

So, according to the court, if you are a news website then potentially there are certain types of story where you should anticipate such material and remove it promptly, even before you get a complaint.

This is a potentially huge workload for busy news sites. One only has to have a look at the type and volume of comment generated by everyone from the Guardian, to the Daily Mail and the likes of Guido Fawkes' blog to see the potential implications of this ruling.

They ought to be united in opposing it, or start hiring more moderators … who know their law.

David Banks is a journalist and media law consultant