Sorry, Sam, but flat murder numbers show nothing (as the population of Detroit is 713,000, and the U.K. is 62 million). You need to look at population.
http://en.wikipedia.org/wiki/List_of_countries_by_intentional_homicide_rate
U.K. murder rate per 100,000 people: 1.2
U.S. murder rate: 4.2...