Yeah, China and other parts of Asia industrializing had a lot to do with it. Another big factor was the loss of empire. Before the war, London was the capital city of an empire that spanned the world. After the war, most of the empire was gone, and the UK was in financial dire straits. People no longer flocked to London looking for opportunity like they did before.

At the same time, the rise of the automobile allowed more people to leave the urban center for the surrounding areas. So even if London were supplying the same degree of economic development, more people could partake in it without actually living within Greater London. Opposed to that, the rising urban areas in Asia were still heavily dependent upon mass transit and foot transport. China has only converted to a car culture within the last 15 years. India is still working toward it. Japan has been one for a while, but their population is so dense and their livable land so limited that they don't have the same options to live away from urban centers.