What I found interesting is the last sentence in the article I read about the raids taking place it was: Just this weekend, hundreds of armed police took part in an exercise simulating a "marauding" terrorist attack on the River Thames.

Link to article: http://www.msn.com/en-us/news/world/major-raids-conducted-after-london-attack-7-arrested/ar-BByCg99?li=BBnb7Kz