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.
More top news
Nakay Kpaka, who starred in series Broadchurch and Grantchester, attacked two women while they slept at house parties.
The Senior Coroner who headed up the struggling West London Coroner's service has been suspended from his post.
Arsonists have been caught on CCTV camera firebombing a Chelsea mansion.