The Crimean War.
Follow my thinking here.
The outbreak of the Crimean war saw the Royal Small Arms factory in Enfield purchase a variety of American gun making machinery. This was the first real adoption of mass production techniques in the UK, and a fledgeling group of gunsmiths from the West Midlands teamed together to create a new factory in Small Heath, Birmingham, the formation of the Birmingham Small Arms company. (BSA). This factory and the manufacturing processes were based on the interchangeability of parts.
After the Crimean War there broke out an unusually long period of widespread European peace, not good for a gun manufacturer at the best of times, but fortunately, there were ongoing colonial fights to keep them going for a while. However by 1879 the factory was idle… then some bugger figured out that the machinery for making guns with interchangeable parts was rather good for making bicycles too… so they did!
So, we witnessed a huge boost in British manufacturing, the wide scale adoption of mass production techniques, producing massive numbers of bicycles (which became adopted as very much the mass personal transportation and recreational activity of the day), then easily converted back to war production in order to help us win WW1, subsequently leading to BSA’s post war expansion into mass motorbike production, back to guns and bombs for WW2 with the massive production facilities then leading into post war production of more bicycles motorbikes, cars, aircraft etc. an entire tourist economy being built around the people touring the countryside on bikes, motorbikes, cars and then foreign holidays.
all because of the steps taken to produce guns for the Crimean war