Moe
The ruling British classes, once brought up quite ignorantly to view the rest of the world as their garden in the days of empire were also taught never to show their superiority, but it showed through all the same and got up educated people's noses. Something similar is there with modern Americans except that they are more open about it.
I don't know where this started, but the British have loved to make losers into their heroes; I think it goes way further back than socialism. Americans are seens as winners: ww2 expressions like "over-sexed, over-paid, and over here" sum that up, and sneering at rich American tourists who want to 'take in' England in a week, these are the winners 'we' resent.
It's provbably not about Americans and Britain though, Britains and Irish, Russians and Georgians, Germans and Austrians, Spaniards and Catalonians - such resentments are smouldering in the embers of every empire.
philo