An angular analysis of the $B0\to K\ast 0e+e-$ decay is performed using a data sample corresponding to an integrated luminosity of $9 fb-1$ of $pp$ collisions collected with the LHCb experiment. The analysis is conducted in the very low dielectron mass squared ($q2$) interval between $0.0008$ and $0.257 GeV2$, where the rate is dominated by the $B0\to K\ast 0\gamma$ transition with a virtual photon. The fraction of longitudinal polarisation of the $K\ast 0$ meson, $FL$, is measured to be $FL=(4.4\pm 2.6\pm 1.4)\%$, where the first uncertainty is statistical and the second systematic. The $ATRe$ observable, which is related to the lepton forward-backward asymmetry, is measured to be $ATRe=-0.06\pm 0.08\pm 0.02$. The $AT(2)$ and $ATIm$ transverse asymmetries, which are sensitive to the virtual photon polarisation, are found to be $AT(2)=0.11\pm 0.10 \pm 0.02$ and $ATIm=0.02\pm 0.10\pm 0.01$. The results are consistent with Standard Model predictions and provide the world's best constraint on the $b\to s\gamma$ photon polarisation.