The website MCV released an artcle about the relationship between violent video games and knife epidemic which was said by Boris Johnson mayor of london.
The details are as below:

Violent games encourage knife crime, says Boris Johnson
Mayor of London cites 'violent video games' as an influence in rising knife epidemic
London Mayor Boris Johnson has pointed the finger at violent video games for being a cause of knife crime in the Capital.
In a piece railing against 'London's knife crisis' written for thelondonpaper, the blunder-prone public figure writes: "We must show young people that knives are not cool, and for that we need positive role models."
"I want to counteract the damaging influences drug-addled celebrities and violent video games and the lure of the life in the gang by providing opportunities."
It's not the first time Boris has been critical of video games.
In January, 2007, he posted a piece on his website entitled 'The writing is on the wall, computer games rot the brain'.

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Resource: MCV