ALMA Band 6 (1.3 mm) image of HD 202628 (Faramaz et al. 2019), as an example of the ALMA data used in this paper (Sect. 2.2.1). North is up, and east is left. The debris disc is well resolved and clearly eccentric, with the host star (crosshairs) offset from the geometric centre of the disc. Considering the pericentre, q_i, and apocentre, Q_i, of the disc inner edge, plus equivalent values q_o and Q_o for the outer edge, yields the minimum mass of a single planet required to sculpt and stir the disc within the system lifetime (Sects. 3.1 and 4.2). This minimum-mass planet would have the orbit shown by the grey line; alternatively, a higher-mass planet located farther inwards could also sculpt and stir the disc. It is unclear whether the bright point in the north-east part of the ring is a background object or associated with the system (Faramaz et al. 2019).