19 December 2012 Last updated at 05:11 ET

Article written by Nick Robinson Political editor

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Why the Andrew Mitchell 'plebgate' story matters

 

What began as a story about what was really said became a story about who leaked a police log but it is now much more serious than that.

The Metropolitan Police say they are investigating allegations against a serving police officer of fabricating evidence against someone who was, at the time, a cabinet minister. What's more, they say that they will investigate conspiracy if any evidence emerges.

We now know that no member of the public corroborated the police version of what Andrew Mitchell said. Contrary to what is stated in the police log leaked to the press, the CCTV shown on Channel 4 last night suggests that no-one was there to hear what was said.

What is more, we know that an email which purported to come from a member of the public in fact came from a serving police officer who was not on duty or even present in Downing Street at the time.

The email was sent before any account of what happened reached the media and yet is remarkably similar to the police log both in the events it describes and the phrases it alleges Mr Mitchell used.

Hold on, some will say, the two officers who reported what Mr Mitchell said are both still sticking to their story and their boss, the head of the Metropolitan Police, insists he's seen nothing which challenges their story.

That, though, does not answer the questions which the Met has now admitted are "extremely serious" and the subject of "a thorough and well resourced investigation" :

• Why did the email get written?
• How did the officer who wrote it know what was in the police log?
• Did he talk to the officers involved, to their superiors or to the Police Federation?

There are many who, I know, are sick of the story of "plebgate" or who long ago took the view that, whatever words Andrew Mitchell actually used, the minister behaved in a way that no member of the public would get away with.

The reason I believe it matters is that this row is now about the power of politicians, the police and the press - the issues which, you may recall, triggered the Leveson inquiry.