Can patterns of diachronic sound change within a language variety predict phonetic variability useful for distinguishing speakers? Standard Southern British English monophthongs are analysed to test whether individuals differ more widely in their realisation of sounds undergoing change than stable sounds. Read speech of 50 male speakers aged 18-25 is analysed. The changing vowels /æ,ʊ uː/ are compared with the stable /iː,ɑː,ɔː/. The data confirm the stability of /iː,ɑː,ɔː/, the fact that /ʊ,uː/ indeed have fronted and that the articulation of /æ/ has become more open. Results from discriminant analysis based on F1 and F2 frequencies, however, do not show a straightforward pattern: no discrete difference is observed between changing and stable vowels. It is suggested that high variability in some speakers obscures the effect of large between-speaker variability in changing vowels.