This one is interesting in that Johnny doesn't live in the UK, but Rowling does. Since she is mentioned in the original article, I wonder if she is considering a similar suit or just having her mentioned in the article will help his case.
In order for a claimant to succeed in a defamation lawsuit, the following must be true:
The statement in question must be a negative false statement of fact;
The statement in question identifies or refers to the claimant;
The statement in question was published.
Acceptable defenses in a U.K. defamation case are:
Justification (truth);
Qualified Privilege (defendant did not act with malice; reporting of proceedings in a foreign court);
Reynolds Privilege (subject matter was sufficiently in the public interest, journalists researched carefully and behaved responsibly);
Absolute Privilege (fair and accurate reporting of domestic court proceedings); or
Fair Comment (matters of legitimate public concern that constitutes a comment, rather than a statement of fact, which an honest person could make on those matters [i.e. critique or film review]).
In the UK, most defamation cases are settled out of court. If parties can agree, the jury can be dispensed in favor of a single judge. There are statutory provisions permitting a trial by a judge alone, if the case involves a significant number of documents or complex technical issues.
LIBEL TOURISM AND THE UK
Why is the UK known as the “libel tourism” capitol of the world? Aside from a “no win, no fee” contingency, damages awarded to libel claimants are high. As the term suggests, libel tourism is the practice of non-UK citizens or companies using UK courts for defamation cases because existing laws in the British Commonwealth favor plaintiffs. However, since the passing of the UK Defamation Act of 2013, libel tourism is expected to decrease.