The decline of agriculture
A quarter of all British men were farm workers in 1850. Britain's agriculture was still her most important trade. But industry was growing all the time. And after 1875, farming hit bad times.
Food from abroad was the main cause of the decline of agriculture. As her population grew, Britain had to import more of her food. And by the 1880s, imported wheat (mainly from the U.S.A.) was cheaper than wheat grown in England. British farmers could not get a decent price for the crops they grew.
Why was wheat from the U.S.A. cheaper to buy in London than wheat grown 20 miles away in Essex? The first answer is that land was very cheap on the American prairies. (English farmers had to pay rent.) Secondly, there were more machines (e.g. binders and steam ploughs) in the U.S.A., so they did not need so many men. And thirdly, with railways and steamships, transport costs were low.
Low prices meant low profits for farmers. Landlords had to charge lower rents, so they were worse off too. Many farmers stopped growing wheat, and kept cattle and sheep instead. Then, in the 1880s and 1890s, frozen mutton and beef began to arrive from abroad, and meat prices fell as well. A lot of farmers went out of business. Those who did not needed fewer labourers. Farm workers and their families made for the towns.
Walter Robson: Britain 1750 – 1900; Oxford University Press, 1993/2002, page 59