Why did Keith Wallis plead guilty to a crime he didn't commit?

On 10th January 2014 Keith Wallis, of the Metropolitan Police's Diplomatic Protection Group, pleaded guilty to a charge of "misconduct in public office".

See, for example, 'Plebgate' PC Keith Wallis pleads guilty to misconduct

The media, who were aware that Wallis had admitted sending an email that was untrue not least becuase he pretended to be a member of the public and pretended to have seen things that he didn't see, expected a guilty plea.

So far so unremarkable.

Nobody so far as I'm aware has asked the question, "Why did Keith Wallis plead guilty to a crime he didn't commit?".

Let's look at the Crown Prosecution Service Guidance on Misconduct in Public Office, which is to be found here:
Misconduct in Public Office

The elements of the common law crime of misconduct in public office are listed as follows:

• A public officer
• Acting as such
• Wilful neglect or misconduct
• Without reasonable excuse or justification

Let's look at each element in turn:

• Was Keith Wallis a public officer? - Yes
• Was Keith Wallis acting as a public officer when he sent the false email? - No
• Was Keith Wallis's misconduct wilful? - Yes, he admitted as much
• Was Keith Wallis's misconduct without reasonable excuse or justification? - Yes

Keith Wallis was off duty when he sent the false email.

He was not, in the terminology of the CPS Guidance, "acting as such".

One of the essential elements for a charge of misconduct in public office was absent.

There you have it.

It's worth repeating because it's a key issue.

One of the essential elements of the offence of misconduct in public office is missing.

Did neither Keith Wallis's solicitor nor barrister spot that?

If they had spotted this glaring flaw in the Crown's case you would expect a simple interaction with the judge something as follows (assuming the matter ever got to court):

1. QC for Wallis: My Lord I ask you to direct the jury to find the defendant, Keith Wallis, not guilty since one of the essential elements of the charge of misconduct in public office is absent.
2. Judge: Mr. QC you are absolutely right.
3. Judge: Members of the jury I direct you to find the defendant, Keith Wallis, not guilty on the charge of misconduct in public office
4. Clerk to the Court: Mr/Ms Foreman of the Jury, what is your verdict?
5. Foreman of the Jury: Not guilty

Did Keith Wallis's legal team not advise him that he was clearly not guilty of the charge of misconduct in public office?

Whatever the nature of the interaction between Mr. Wallis and his legal team, it is clear that he wasn't guility of "misconduct in public office" since one of the essential elements of the offence is missing.

So, the question remains "Why did Keith Wallis plead guilty to a crime that he didn't commit?"

Why does anyone plead guilty to a crime that they don't commit?

Before I attempt to answer those questions I'll consider the related question, "Why did the Crown Prosecution Service charge Keith Wallis with a crime he didn't commit?".