This article documents the historical development and synchronic variation of so-called “/h/ insertion” (/h/ before vowel-initial words such as apple, under, etc.). It argues that the maintenance of /h/ insertion in post-colonial English varieties around the world provides an ideal opportunity for research on language change under dialect contact scenarios involving British donors and other dialects. After an assessment of regional distribution patterns in current World Englishes, it presents some first findings from a large-scale quantitative analysis of Tristan da Cunha English, where /h/ insertion, firmly attested yet nearing obsolescence in British English, has survived into the 21st century. The quantitative analysis provides important insights into donor attribution and competition-selection processes that accompany dialect contact and koinéization, with special reference to theoretical concepts such as colonial lag, feature pool formation and founder effects. A holistic application of the concept of colonial lag to post-colonial English varieties needs to be refined and critically assessed. It is argued that entire linguistic systems (in the form of koinés) are not conservative as such but that arrested language (and dialect) change operates on a feature-specific level instead.