We present a sequence of eight spectropolarimetric observations monitoring the geometric evolution of the late phase of the major 2012 outburst of SN 2009ip .
These were acquired with the FORS2 polarimeter mounted on ESO VLT .
The continuum was polarised at 0.3-0.8 % throughout the observations , showing that the photosphere deviated substantially from spherical symmetry by 10-15 % .
Significant line polarisation is detected for both hydrogen and helium at high velocities .
The similarity in the polarised signal between these elements indicates that they form in the same location in the ejecta .
The line polarisation ( p \sim 1-1.5 % ) at low velocities revealed the presence of a highly-aspherical hydrogen and helium rich circumstellar medium ( CSM ) .
Monte Carlo simulations of the observed polarimetry were performed in an effort to constrain the shape of the CSM .
The simulations imply that the polarimetry can be understood within the framework of a disk-like CSM inclined by 14 \pm 2 ^ { \circ } out of the line of sight , obscuring the photosphere only at certain epochs .
The varying temporal evolution of polarisation at high and low velocities indicated that the fast-moving ejecta expanded with a preferred direction orthogonal to that of the CSM .