A decade of surveys has hinted at a possible higher occurrence rate of debris discs in systems hosting low mass planets. This could be due to common favourable forming conditions for rocky planets close in and planetesimals at large radii. In this paper we present the first resolved millimetre study of the debris disc in the 4.6 Gyr old multiplanet system 61 Vir, combining ALMA and JCMT data at 0.86 mm. We fit the data using a parametric disc model, finding that the disc of planetesimals extends from 30 AU to at least 150 AU, with a surface density distribution of millimetre sized grains with a power law slope of 0.1$\mathrm{<mrow\; data-mjx-texclass="ORD">-0.8</mrow><mrow\; data-mjx-texclass="ORD">+1.1</mrow>}$. We also present a numerical collisional model that can predict the evolution of the surface density of millimetre grains for a given primordial disc, finding that it does not necessarily have the same radial profile as the total mass surface density (as previous studies suggested for the optical depth), with the former being flatter. Finally, we find that if the planetesimal disc was stirred at 150 AU by an additional unseen planet, that planet should be more massive than 10 M$\mathrm{<mrow\; data-mjx-texclass="ORD">\oplus </mrow>}$ and lie between 10-20 AU. Lower planet masses and semi-major axes down to 4 AU are possible for eccentricities $\gg$ 0.1.