A long-accepted tenet of town planners is that industry should be separated from residential areas. It was pointed out that when industry and housing are mixed together, each interferes with the proper functioning of the other: industrial nuisance often makes a healthy life impossible for people living near to factories, while in its turn the housing often prevents the efficient layout of factories. The grim industrial cities of the north were cited, and one particular photograph of cotton mills and by-law housing at Oldham in Lancashire was published dozens of times, with other even more horrifying ones of the Potteries with wretched housing crouching at the base of bottle kilns.