  Long gamma-ray burst GRB 191016A was a bright and slow rising burst that was
detected by the \textit{Swift} satellite and followed up by ground based
Liverpool Telescope (LT). LT follow-up started $2411$-s after the
\textit{Swift} Burst Alert Telescope (BAT) trigger using imager IO:O around the
time of the late optical peak. From $3987-7687$-s, we used the LT polarimeter
RINGO3 to make polarimetric and photometric observations of the GRB
simultaneously in the $V,R$ and $I$ bands. The combined optical light curve
shows an initial late peak followed by a decline until 6147-s, 6087-s, and
5247-s for $I,R$ and $V$ filters respectively followed by a flattening phase.
There is evidence of polarization at all phases including polarization ($P =
14.6 \pm 7.2 \%$) which is coincident with the start of the flattening phase.
The combination of the light curve morphology and polarization measurement
favours an energy injection scenario where slower magnetised ejecta from the
central engine catches up with the decelerating blast wave. We calculate the
minimum energy injection to be $\Delta E / E>0.36$. At a later time combining
the optical light curve from BOOTES (reported via GCN) and IO:O we see evidence
of a jet break with jet opening angle 2 \degree.
