Speaking at the opening of a library at South Ruislip in north west London, Mr Johnson said people could not swear at police and expect to get away with it.
If I read the papers correctly there was a proposal to arrest Mr Mitchell for what he said. That seems to be wholly common-sensical.
The public order act does allow for police officers' discretion in this matter. They've obviously decided not to go ahead with it.
But it shows the gravity of this offence.
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John Nolan, who was found with cigarettes and two lighters, suffered burns on 65% of his body after being alight for around six minutes.
Known as Pily she died in January, seven months after the disaster, having suffered a stroke.
The shake-up also aims to smash the "myth" that officers cannot pursue riders who are not wearing helmets.