Recent acoustic studies have provided evidence that /u/ (goose) and /ʊ/ (foot) have fronted in the standard accent of England in the last fifty years, but what is less clear is whether this fronting is due entirely to a repositioning of the tongue or whether it has been accompanied by an unrounding of the lips. Four experiments were carried out to shed light on this issue. An acoustic study of anticipatory coarticulation in /s/ in the first of these suggested a similar degree of lip-protrusion for young speakers whose F2 of /u/ was raised compared with that of older speakers. Compatibly, judgments of lip-rounding elicited from cross-dubbed auditory-visual stimuli and an analysis of lip movement showed young speakers' /u/ to be produced with rounded lips. Their tongue positions and movements in the final experiment were found to be almost as advanced for /u/ as for /i/ (fleece) and nearer to a central position for lax /ʊ/ (foot). Taken together, these results confirm firstly, that the diachronic shift in /u/ has involved a realignment of the tongue, but not of the lips; and secondly, that the diachronic shift in /ʊ/ is likely to be a more recent innovation than that of its tense counterpart.