  In order to investigate the effects of vacuum polarisation on mass inflation
singularities, we study a simple toy model of a charged black hole with cross
flowing radial null dust which is homogeneous in the black hole interior. In
the region $r^2 \ll e^2$ we find an approximate analytic solution to the
classical field equations. The renormalized stress-energy tensor is evaluated
on this background and we find the vacuum polarisation backreaction corrections
to the mass function $m(r)$. Asymptotic analysis of the semiclassical mass
function shows that the mass inflation singularity is much stronger in the
presence of vacuum polarisation than in the classical case.
