InFin, sorry, but you're wrong. Libel
can be both a tort and a crime. If you have access to a Law library, check
Adams (1888) 22 QBD 66 and
Holbrook (1878) 4 QBD 42 at 46.
...In tort, the gist of the matter is the loss of the the plaintiff's reputation and this occurs through publication to a third party; but a principle reason why libel is indictable is the danger to the public peace (See Holbrook) and this may obviously be even greater where the publication is to the prosecutor himself than where it is to another...
The truth of the defamatory statement affords a complete defence (justification) in tort but in crime the defendant must prove not only that the statement is true but that it is for the public benefit that it be published. This is the effect of the Libel Act 1843, modifying the common law under which it is probable that truth was not a defence to the indictment.
(Smith & Hogan, Criminal Law 5th. Edition)
stagger, the only difference I was trying to point out (adding in the stuff about slander over-complicated my post, sorry!) was that a libel does not need to be published to a third party. I can't currently locate the precedent, but I believe I've seen that intent to publish a libel (having shown it to the plaintiff only) is also considered a libel.