Left panel: position-velocity (PV) diagram of the SiO emission extracted from a cut (as wide as the synthesised beam) at a position angle of 30° across the putative disc major axis (see Fig. 3 – position offsets are positive to north-east). The grey contours are at the 10, 15, 20, 25 and 30 mJy beam⁻¹ level to highlight the structure. The black dotted line is a guide to indicate the excess of high velocity emission at small spatial offsets. Centre panel: observed SiO PV as the left plot (colour map with grey contour at a 10 mJy beam⁻¹ level) overlaid with pure Keplerian rotation profiles for a 200 au radius disc around a 20, 30 and 40 M_⊙ (inner dashed, solid, outer dashed lines) O-type YSO, when considering an inclination of 70° (de Wit et al. 2011). The disc outer radius was limited to 200 au such that the lowest velocities roughly matched the kink in the observed data. The disc lines here represent only the high-velocity emission. Right panel: observed SiO PV as the left and central plots but overlaid with the contours of pure Keplerian rotation profiles for a disc around a 10, 20, 30 M_⊙ (inner dashed, solid, outer dashed lines) OB-type YSO rotating in the opposite direction to that plotted in the central panel (using an inclination of 70°). The disc outer radius was set to 650 au in an attempt to match the low velocity spurs at large spatial offsets. The spatial and velocityresolution are indicated by the black bars at the bottom left of all plots. Note the central figure indicates the north-east and south-west offset directions that relate to the cut along the disc direction in Fig. 3.