  HR 4796A is surrounded by a well-structured and very bright circumstellar
disc shaped like an annulus with many interesting features: very sharp inner
and outer edges, brightness asymmetries, centre offset, and suspected
distortions in the ring. We aim to constrain the properties of the dust
surrounding the star HR 4796A, in particular the grain size and composition. We
also want to confirm and refine the morphological parameters derived from
previous scattered light observations, and reveal the dust spatial extent in
regions unexplored so far due to their proximity to the star. We have obtained
new images in polarised light of the binary system HR 4796A and B in the Ks and
Lp band with the NaCo instrument at the Very Large Telescope (VLT). In
addition, we revisit two archival data sets obtained in the Lp band with that
same instrument and at 2.2 microns with the NICMOS instrument on the Hubble
Space Telescope. We analyse these observations with simulations using the
radiative transfer code MCFOST to investigate the dust properties. We explore a
grid of models with various dust compositions and sizes in a Bayesian approach.
We detect the disc in polarised light in the Ks band and reveal for the first
time the innermost regions down to $0.3"$ along the semi-minor axis. We measure
a polarised fraction of $29\%\pm8\%$ in the two disc ansae, with a maximum
occurring more than $13^\circ$ westwards from the ansae. A very pronounced
brightness asymmetry between the north-west and south-east side is detected.
This contradicts the asymmetry previously reported in all images of the disc in
unpolarised light at wavelengths smaller than or equal to 2.2 microns and is
inconsistent with the predicted scattered light from spherical grains using the
Mie theory. Our modelling suggests the north-west side is most likely inclined
towards the Earth, contrary to previous conclusions.
