With the sun beating down on the strange and exotic-looking meats on sale — some dripping blood, some heavily smoked and impossible to identify — the sights and sounds at this London market are straight out of Africa. Skinned goat carcasses dangle overhead, blackened cow heads and lamb brains are lined up in trays, while baskets tucked in darker corners brim with yellowing strips of cured flesh. Nearby, women hawk spices, cassava and yams, as men in shacks offer cheap airline tickets to Nigeria, Ghana and Cameroon, as well as cash transfers back to family members still living on the...