"London was a powerful magnet for largest population." Explain

London attracted large number of migrants though earlier industrial cities like Manchester and Leeds also had a large migrant population.
19th century London had a large population consisting of clerks, shopkeepers, artisans, soldiers, casual labours, street sellers, beggars, etc.
With the growth of population as well as industries, people from all parts began to pour in London. Apart from London dockyards, five major types of industries employed large numbers of people; most of whom came from suburbs.
In 19th century, London’s population multiplied four fold in 70 years between 1810-1880, increasing from 1 million to 4 million.