This study presents a large-scale investigation of sociolinguistic variation in the phonetic realisation and phonemic status of FOOT and STRUT in Manchester English. As a Northern dialect of English, Manchester speakers typically lack the distinction between the FOOT and STRUT vowels, such that 'stud' and 'stood' are homophones. The data in the present study reveal that, despite the vast majority of speakers having no difference in production and perception, there is variation both in the phonemic status and the phonetic realisation of the two vowel classes within the speech community. The study is based on the acoustic analysis of a sample of 123 speakers stratified by age, gender, socio-economic status, and ethnicity, recorded in sociolinguistic interviews, supplemented with wordlist reading and minimal-pair tests. Our approach to the analysis considers the vowel classes both as one phoneme, and as the two split lexical sets. The acoustic measurements reveal that tokens in the STRUT category show a monotonic pattern of social class stratification, with higher social classes showing higher F1 values, i.e., having a lower tongue position. The minimal-pair tests of the FOOT-STRUT distinction reveal that although for most speakers there is no phonemic distinction, for 8 speakers in the two highest socio-economic levels in the sample, the two vowels do form separate categories. This is confirmed by the acoustic measurements of their vowel tokens: there is clear phonetic separation between the two vocalic categories in phonetic space. Interestingly, even when these 8 speakers are removed from the sample, regression analysis shows that for the sample as a whole, vowel category (i.e., STRUT vs. FOOT) continues to have a significant effect, with STRUT tokens having a higher F1 mean (lower tongue position). This holds in cases where there is complete overlap between the two vowels in phonetic space. We explore the possibility that this may be due to the different phonological environment in which the two vowel classes tend to be found and that it may shed light on the underlying mechanisms of the historical split between the two vowel classes in the south of England.