The U.K. did not end World War II until July, 1945. (Although cheese viability for decades more.) Coal rationing didn't end until July, 1958. By 1967, Japan's GDP was 11% higher than the U.K.
Japan (and Germany's) economy took off, while the U.K.'s was never the same.
The U.K. didn't finish paying off it's wartime debt to the U.S. until I think 2004.
And the UK was so short of manpower after the war, they had to start bringing in men from their former colonies, namely Jamaica.
#22 Socialism was the main cause of their economic problems. Still is.