After a Channel 4 News and Dispatches investigation questions the account recorded in a police log and results in calls for an investigation, Michael Crick answers the key questions on the row.

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Why did Andrew Mitchell lose his job?

The argument over whether Andrew Mitchell called a police officer a "f****** pleb" dragged on for more than a month: the incident happened on 19 September, and he resigned on 19 October.

There was huge pressure on him during that time. It was very embarrassing for the Conservative party and was seized on by political opponents. But the reason why the particular phrase "you f****** pleb" was so dangerous to the Conservatives was that it reinforced the negative image of them being public school toffs who looked down on ordinary people.

In the end he lost his job because effectively he could no longer operate as chief whip. It's a hugely important position - the chief whip is responsible for disciplining back benchers, making sure everyone votes for government and relaying members' views to the prime minister and vice versa. Basically he had lost the confidence of back benchers, many of whom thought the swearing was the kind of thing Mr Mitchell could easily have done.

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What does the world know now as result of the investigation?

Two things really. Firstly, Channel 4 News and Dispatches have shown the world, for the first time, three different rolls of CCTV footage from the afternoon of Thursday 19 September. In several ways that footage seems to undermine the police log of events that was leaked to the Telegraph the following week. Although there's no audio, the body movements don't suggest aggressive outbursts by Mr Mitchell.

But perhaps most importantly, the Telegraph log says there were eyewitnesses to the incident who were "visibly shocked". The CCTV footage shows just one man wandering up and down, but he doesn't appear to be showing any particular interest in the incident, or to be shocked. That does undermine the police log.

Secondly, we now know that an email was sent from a man in Ruislip, to his MP John Randall - who coincidentally was and still is deputy chief whip - with an account very similar to the police log published in the Telegraph. This had a big impact within Downing Street, and I think probably persuaded Mr Randall that Mr Mitchell should go.

We also know the man who wrote this email was a serving police officer, which suggests an effort by one or more policemen to corroborate what had been written in the police log. But crucially, the man who wrote this email has subsequently twice - by telephone and face to face with me - said that he wasn't there. This shows that there is on the face of it, evidence of an attempt to fabricate an account against Mr Mitchell.

Why did the Sir Jeremy Heywood inquiry not find this out?

It's extraordinary that it didn't. They sent Mr Randall round to the eyewitness's house, but he didn't manage to discover what his background was.

It is hugely embarrassing to Sir Jeremy that this happened. David Cameron had to go off to New York after Sir Jeremy had carried out his inquiry and when he discovered what we found out three months later, he was fuming. That's why he was keen for our story to go ahead. The prime minister was watching our item with great interest last night, I hear.

Andrew Mitchell 'plebgate' row: the key questions (G)

What has been revealed about the relationship between police and media?

Many of the issues raised during the Leveson inquiry regarding the relationship between the police and the media come up here. How did the Telegraph get the police log? How did the Sun get the initial story that appeared on 20 September? And can the police be trusted? This story also brings together some of the issues of the year: can we trust police logs, or are they as dodgy as they were 20 years ago in Hillsborough?

For the media, it raises similar questions to the reporting of Lord McAlpine in connection to north Wales abuse scandal, which happened not long after: the media can get into a frenzy, and almost hope something is the case. But, as with the Andrew Mitchell story, close examination shows the story was not as straightforward.

Perhaps the conclusions we need to draw are that journalists should be a little bit more careful in some of the stories they run, and not hunt in packs.

Is this just about restoring Andrew Mitchell's reputation?

Obviously Mr Mitchell hopes to do that. He is very keen to restore his reputation of course. But I think it's much more important in a way, for the Conservative party to wipe this word out. Whether they'll ever entirely do that, I'm not sure. But the questions raised about the accuracy of the police log will make it much harder for their opponents to use the "pleb" word against them.

We don't yet know what happened exactly, we can't really be sure either way because of the lack of audio in the CCTV footage. But "plebgate" will feature very prominently in Mr Mitchell's obituary, no doubt.

What is the mood within the Conservative Party?

Undoubtedly Mr Mitchell does have people who are not his friends. There is also a sense of nervousness about bringing this story back onto the front pages - some may have preferred to let sleeping dogs lie. But many MPs, and not just Conservatives, believe there should be an inquiry into what happened.

Will Andrew Mitchell get his job back?

The prime minister is pretty sympathetic to Mr Mitchell now. Once the police inquiry has made its course, assuming no new evidence comes up, I think Andrew Mitchell will get another job in government. It depends what vacancies come up, but I think he would like a proper ministerial portfolio, perhaps as foreign secretary if that becomes available. But there's no denying that a lot of what we managed to reveal has vindicated him.