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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The 90-year-old victim watched in horror from her bed as the thief climbed in through her bedroom window.
The remains of Sophie Lionnet, 21, were discovered in a garden at a house in Southfields, south-west London last year.
Port drugged and raped four young men and dumped their bodies near his home in Barking, east London.