This article presents a systematic analysis of morphosyntactic variation in London English, investigating was/were variation in the speech of adolescents and elderly speakers in a multicultural inner London area and a less diverse outer London area. In outer London, dialect leveling to a mixed was/weren't system is well underway, as in many other areas of the U.K. Negative weren't is frequent and a grammaticalized invariant weren't it tag is developing. In inner London, variation in adolescent speech is strongly influenced by ethnicity, resulting in a lower overall frequency of was leveling and, in negative contexts, a mixed pattern of leveling to both wasn't and weren't. The patterns of variation of Anglo “heritage” inner London adolescents differ both from elderly speakers in the same area and from their peers in outer London. Our analysis confirms the need for socially realistic models of language change that take account of the social diversity of large multicultural urban cities.