  The debris disc around HD 172555 was recently imaged in near-infrared
polarised scattered light by the Very Large Telescope's Spectro-Polarimetric
High-contrast Exoplanet REsearch instrument. Here we present optical aperture
polarisation measurements of HD 172555 by the HIgh Precision Polarimetric
Instrument (HIPPI), and its successor HIPPI-2 on the Anglo-Australian
Telescope. We seek to refine constraints on the disc's constituent dust grains
by combining our polarimetric measurements with available infrared and
millimetre photometry to model the scattered light and continuum emission from
the disc. We model the disc using the 3D radiative transfer code Hyperion,
assuming the orientation and extent of the disc as obtained from the SPHERE
observation. After correction for the interstellar medium contribution, our
multi-wavelength HIPPI/-2 observations (both magnitude and orientation) are
consistent with the recent SPHERE polarisation measurement with a fractional
polarisation $p = 62.4 \pm 5.2$~ppm at 722.3 nm, and a position angle $\theta =
67 \pm 3^{\circ}$. The multi-wavelength polarisation can be adequately
replicated by compact, spherical dust grains (i.e. from Mie theory) that are
around 1.2 $\mu$m in size, assuming astronomical silicate composition, or 3.9
$\mu$m assuming a composition derived from radiative transfer modelling of the
disc. We were thus able to reproduce both the spatially resolved disc emission
and polarisation with a single grain composition model and size distribution.
