An estimated 65,000 Greek citizens migrated to the UK in 2010–2016, many of whom with the prospects of long-term settlement and with a view to provide better socioeconomic and educational opportunities to their children. Their arrival was felt across many sections of life both within and beyond the country’s pre-existing Greek-speaking communities. In this article, I present findings on how the arrival of Greek pupils, parents and qualified teachers diversified Greek complementary schools, which were previously run primarily by and for the Greek Cypriot community, and on the critical role language played in the process. Drawing on data from a set of semi-structured interviews with teachers and placing my investigation against the historical backdrop of migration from Greece and Cyprus to the UK, I show how teachers portrayed post-2010 migration as a much needed, albeit not always welcome, boost in ethnocultural vitality; how it helped to perpetuate the hierarchisation of standardised and non-standardised varieties of Greek and the stigmatisation of the multilingual and multidialectal repertoires of people with a Greek Cypriot background; and, how it put a strain on the ties that have historically brought the Greek and Greek Cypriot communities together in the context of the UK diaspora.