England certainly handed the Super power/Empire batten to America after ww2 but the world police thing is more driven from America by Americans.
Can you name a conflict America entered because the UN requested you to? I can only name one for Australia and that was East Timor (was very successful in every way as well).
Even going back to Vietnam that is a war that is ingrained with our generation, America and its allies were supporting a Govt that Buddhist monks were setting themselves on fire in protest of. Certainly not what a "Police" force should be doing.
I know my Father- a SGT whilst in Vietnam, has never forgiven the US and Australian Government for that war .
Viet Nam is a very dicey subject for me..governments want war not it's peoples..Kent State and over the border were what it mean to me as a child; my uncle was a Marine with Honorable Discharge, a heroin habit..gee thanks Uncle Sam! We lost him one Thanksgiving- he was double patching it by then. if it weren't for Viet Nam, i wouldn't be here as well; so dicey.