[sillyquiet]

No OP's correct, the US surpassed the UK both in population and in GDP sometime around the middle of the 19th century.

[fmajid]

The US overtook the UK in 1860, but overtaking the entire British Empire was closer to 1900.

[ghaff]

I think the point is that looking at the UK in a vacuum, outside the context of colonies like India, Kenya, Singapore, etc., is probably misleading.