From the later eighteenth century, marked by James Watt's improved steam engine of around 1769, mechanised production and the factory system spread rapidly across Britain. Steam power freed industry from waterwheel sites and concentrated it in towns, drawing unprecedented numbers of rural migrants into Manchester, Leeds, Glasgow and similar centres. The result was explosive, unregulated urban growth, with overcrowded back-to-back housing, polluted air and water, and recurrent epidemics.
It created the squalid, congested industrial city whose sanitary and housing crises provoked the public-health acts, housing reform and the whole apparatus of modern town planning that grew up to address them.