  Long gamma ray bursts (GRBs) are produced by the collapse of some very
massive stars, which emit ultra-relativistic jets. When the jets collide with
the interstellar medium they decelerate and generate the so-called afterglow
emission, which has been observed to be polarised. In this work we study the
polarimetric evolution of GRB 210610B afterglow, at $z = 1.1341$. This allows
to evaluate the role of geometric and/or magnetic mechanisms in the GRB
afterglow polarisation. We observed GRB 210610B using imaging polarimetry with
CAFOS on the 2.2 m Calar Alto Telescope and FORS2 on the 4 $\times$ 8.1 m Very
Large Telescope. Complementary optical spectroscopy was obtained with OSIRIS on
the 10.4 m Gran Telescopio Canarias. We study the GRB light-curve from X-rays
to optical bands and the Spectral Energy Distribution (SED). This allows us to
strongly constrain the line-of-sight extinction. Finally, we study the GRB host
galaxy using optical/NIR data to fit the SED and derive its integrated
properties. GRB 210610B had a bright afterglow with a negligible line-of-sight
extinction. Polarimetry was obtained at three epochs: during an early plateau
phase, at the time when the light curve breaks, and after the light curve
steepened. We observe an initial polarisation of $\sim 4\%$ that goes to zero
at the time of the break, and then increases again to $\sim 2\%$ with a change
of the position angle of $54 \pm 9$ deg. The spectrum show features with very
low equivalent widths, indicating a small amount of material in the
line-of-sight within the host. The lack of dust and the low amount of material
on the line-of-sight to GRB 210610B allow us to study the intrinsic
polarisation of the GRB optical afterglow. We find the GRB polarisation signals
are consistent with ordered magnetic fields in refreshed shock or/and
hydrodynamics-scale turbulent fields in the forward shock.
