I believe the comparison isn't adequate here since the British got massive advantages after WW2.
https://www.youtube.com/watch?v=5uM2cdhfAGA
This is the reason that there's so many rich Russians knocking about e.g. https://old.reddit.com/r/soccer/comments/p83ljc/offshore_adv...
They did well to hold on to it, though.
.. and on all those metrics China came out much worse (the civil war, no marshall plan, proxy war with the US, communism), as well as not having the massive advantage of having been an industrial power long before the war.
This article dates the takeoff to 1978 (Deng), which seems reasonable: https://www.stlouisfed.org/publications/regional-economist/a...
Perhaps the question should be "at what date in the future do we expect the cost of a taxi in London and one in Beijing to equalize"?