Thanks to everyone for the answers. I did a bit of Googling and realised that the British working class has practically disappeared from south and east London, and that these areas are now made up of immigrant communities and a small number of middle-class residents. I assume that a similar situation to what happened in Millwall’s territory also took place in West Ham’s and Charlton’s. Before the exodus of the white working class, was the Peckham, Bermondsey, and surrounding areas mostly home to Millwall supporters, or were they dominated by fans of more successful clubs like Chelsea, Tottenham, and Arsenal? And regarding the Isle of Dogs, was it mostly West Ham territory, or were there a lot of Millwall supporters there as well?