  We present the results of a radio observing campaign on GRB 201216C, combined
with publicly available optical and X-ray data. The detection of very high
energy (VHE, >100GeV) emission by MAGIC makes this the fifth VHE GRB at time of
publication. Comparison between the optical and X-ray light curves show that
GRB 201216C is a dark GRB, i.e. the optical emission is significantly absorbed
and is fainter than expected from the X-ray detections. Our e-MERLIN data also
shows evidence of diffractive interstellar scintillation. We can study the
column density along the line-of-sight to the GRB in both the host galaxy, from
the damped optical light curve, and the Milky Way, via scintillation studies.
We find that the afterglow is best modelled using a jet-cocoon geometry within
a stellar wind environment. Fitting the data with a multi-component model we
estimate that the optical, X-ray and higher-frequency radio data before ~25days
originates from an ultra-relativistic jet with an isotropic equivalent kinetic
energy of (0.6-10)x10^52erg and an opening angle of ~1-9deg. The
lower-frequency radio emission detected by MeerKAT, from day 28 onwards, is
produced by the cocoon with a kinetic energy that is between two and seven
orders of magnitude lower (0.02-50)x10^48erg. The energies of the two
components are comparable to those derived in simulations of such scenarios.
