I think that extreme prosperity like this (another example - Baby Boomers in the US) is a lagging indicator of geopolitical/industrial power.

Britain was prosperous in the 1800s because of colonialism and the industrial revolution. The US was prosperous in the second half of the 1900's because they capitalized on not being decimated by WW2.

IMO Britain's success in this era was actually sustained prosperity driven by the working class, and the failure to maintain global leadership followed from the victorian attitude of the elite.