In terms of civil aviation, the 707 was mass produced on a production line, the Comet was essentially handbuilt. Didn't Boeing reps visit the De Havilland factory during the manufacture of the Comet and declare that they were astounded that anything could be built in such an environment, let alone a jet aircraft?
The British have never been capable of genuine mass production, that's why we innovate.
WW2 did tilt the scales a bit, 1945 = a wrecked Europe and an un-bombed US factory-based economy in full production.
In terms of military aviation, we ran out of money, hence the Phantom, Tornado and the Mk2 Typhoon.