The Great Britain was known to have started the Industrial Revolution due to the series of technological advances in manufacturing taking place. However, due to competition with other countries, the demand for its textile industry started to decrease. It can be primarily attributed to much cheaper labour costs in other countries most likely the United States.
The answer is Factory owners.
The term for the significant growth in population following WWII is the "baby boom." We also now refer to those people as "baby boomers"