It is obvious that the criteria used by many varies here. Oslo?? A couple bars/nightclubs and some Pakistani run hot dog shops that never close does NOT make a 24 hour city.....

London?? A city which is still mostly governed by early 1900's licensing laws (yes they were liberalized a few years back, but residents have made sure that most extensions have not been made - yes there are clubs with late licneses, but they really aren't that late and the proportion of them is no greater than anyother city), and foodwise other than some fast food, perhaps some Turkish Kebabs or a certain chain of Lebanese restaurants you really are hard pressed to get anything to eat late at night (although it is a huge improvement from the past).