Supercop and Gangs

From the BBC:

UK police chiefs have reacted sceptically to plans for US "supercop" Bill Bratton to advise the government.
...
Association of Chief Police Officers' head Sir Hugh Orde said: "I am not sure I want to learn about gangs from an area of America that has 400 of them."

Aside from the nonsense of looking at how many there are currently and not how many there were in the past and how effective Mr Bratton has been at reducing crime (quite effective by all accounts), the numbers are wrong.

Bill Bratton was police chief of both NYC and LA, I'm not sure which one of these Sir Hugh refers to with the 400 gangs. But either way Sir Hugh's numbers ignore an important consideration - population. NYC has an urban population of 18m and LA has 15m. London has only 8m. Yet London has 169 gangs. Taken as a proportion of population that gives 22.2 gangs per million for NYC, 26.6 for LA and 21.125 for London. Not a huge difference there Sir Hugh.