This study focuses on a corpus assembled from commercial recordings of 1929 and 1932 featuring the two British linguists J. R. Firth (1890–1960) and Daniel Jones (1881–1967). The aim is to analyse and quantify differences in the Received Pronunciation (RP) used by the two men, in relation to sociolinguistic and stylistic variation within RP of the period. A systematic acoustic analysis reveals that whereas the vowel systems of the two speakers are closely similar in most respects, there are significant differences in the realizations of the trap, price and dress qualities. We show that each of these has a well-documented history of variation in RP, and find that in each case Firth is employing the higher-class or more prestigious variant, which is a reversal of expectations based on what is known about the social and regional origins of the two. We consider the possible roles of social background, avoidance of regional features and hypercorrection. The outcomes of our work are (i) an illustration of RP used in the interwar period for the purposes of teaching English as a foreign language, (ii) empirical evidence for internal variation within the accent, (iii) additional insights into the stylistic and social correlates of this variation, and (iv) a demonstration that satisfactory formant analyses can be conducted with recordings from as early as the 1920s. Overall, it is hoped that this case-study will both throw light on the ‘standard’ accent of the era and inspire further sociophonetic investigations with legacy recordings.