The Met has been investigating for months how the Sun and the Daily Telegraph obtained the official police log  of the incident, which suggested that Mitchell referred to the police as "plebs". In his resignation letter , Mitchell wrote that "The offending comment and the reason for my apology to the police was my parting remark 'I thought you guys were supposed to fucking help us'. It was obviously wrong of me to use such bad language and I am very sorry about it and grateful to the police officer for accepting my apology."
Scotland Yard said that the officer arrested was not on duty at the time of the incident and that it had found "no evidence to suggest any of the officers involved in the incident were involved in the unauthorised release of information". John Tully, the chairman of the Metropolitan Police Federation, commented  that it was "disappointing to say the least to see the Met take this action."
The arrest has already revived the row over what Mitchell did or did not say. He told  the BBC this morning: "I reiterate once again that the contents of the alleged police logbook are false." In which case, one might ask, will or should action be taken against the officer accused of falsifying the record? And if he did not, will Mitchell ever be forced to account for what he did say?