This paper reports on a phonetic and phonological study of /t/-affrication in spontaneous British English Received Pronunciation. The study is motivated by the uncertainty surrounding plosive affrication in the literature on lenition and fortition. We suggest that a decision as to the status of a given pattern involving affrication in terms of lenition or fortition should be based on thorough phonetic and phonological analysis. We present a phonetic and phonological account of /t/-affrication, which takes into consideration the temporal and spectral characteristics of the sounds involved, as well as their distribution across phonological environments. Crucially, we compare affricated instances of /t/ with aspirated and fricated ones in the same dataset – the former arguably unmarked in this variety, the latter uncontroversially the result of lenition. We argue that the phonetic and phonological characteristics of /t/-affrication presented in this paper are consistent with an account in terms of fortition rather than lenition.