There have been a couple. However, when it does happen it gets a lot of media attention, the most recent incident taking place on Oxford Street, a popular shopp

There have been a couple. However, when it does happen it gets a lot of media attention, the most recent incident taking place on Oxford Street, a popular shopping street in London: http://www.bbc.co.uk/news/uk-england-london-41263926 http://www.bbc.co.uk/news/uk-england-london-41263926