Mitchell has always said he never used the word 'pleb'.

An officer who claims to have heard him say the word wasn't even on duty at the time. Shambles.

Which officer is that? If you mean the one who's been arrested I don't believe he ever said he heard Mitchell say anything, he is alleged to have leaked the official police incident log to the press. It is the log which states Mitchell used the word pleb.

So I'm still struggling to see how Mitchell has a decent case for defamation.

Wrong.

The arrest is for leaking the details of statements to the press by an officer who wasn't on duty at the time but who subsequently had access to the statements, nothing at all to do with what was said by whom.

You should read the news.

http://news.sky.com/story/1026850/andre ... vestigates States here that "A police officer who claimed to have witnessed Andrew Mitchell's Downing Street rant is being investigated by the police watchdog" "The Independent Police Complaints Commission (IPCC) is looking into the "validity" of his account - which helped lead to Mr Mitchell's resignation as Tory Chief Whip in October"

http://news.sky.com/story/1026850/andre ... vestigates States here that "A police officer who claimed to have witnessed Andrew Mitchell's Downing Street rant is being investigated by the police watchdog" "The Independent Police Complaints Commission (IPCC) is looking into the "validity" of his account - which helped lead to Mr Mitchell's resignation as Tory Chief Whip in October"

Even The Guardian reports that the officer seems to have said he witnessed the events when he wasn't on duty and then it is alleged he also misled MPs. If these allegations are founded, it would appear that Mitchell may have been set up for political reasons. The fact that Labour so relentlessly pursued and hounded him on what could prove false allegations should tell the voters all they need to know about Miliband's judgment and ethics.

The Guardian tucks away its report today in a modestly sized article at the bottom of, I think, page 4. A far cry from it's pages on the subject previously. Again, tells you all you need to know about the morals of the left-leaning chattering classes mouthpiece.

None of which gives Mitchell a case for defamation since it is not this officer who recorded the police log.

Or, maybe, The Guardian has realised (as has Mitchell) that, ratrher than this off-duty chap, the issue is really about the contents of the Police log where it is recorded what Mitchell said.
Just a thought.

Your attempts to provoke are merely yawn-inducing.

Just spotted on Twitter:

Eye Spy MP ‏@eyespymp Andrew Mitchell MP told off in Chancery Lane by cab driver for using mobile while cycling: "Get off the phone you moron."

Chancery Lane? Presumably calling his legal advisers to say he's just about to arrive?

Why?
Did he get arrested for using his mobile whilst cycling?