  We calculate the temperature dependent anomalous ac Hall conductance
$\sigma_H(\Omega, T)$ for a two-dimensional chiral p-wave superconductor. This
quantity determines the polar Kerr effect, as it was observed in Sr$_2$RuO$_4$
[J. Xia $et$ $al.$, Phys. Rev. Lett. 97, 167002 (2006)]. We concentrate on a
single band model with arbitrary isotropic dispersion relation subjected to
rare, weak impurities treated in the Born approximation. As we explicitly show
by detailed computation, previously omitted contributions to extrinsic part of
an anomalous Hall response, physically originating from diffractive skew
scattering on quantum impurity complexes, appear to the leading order in
impurity concentration. By direct comparison with published results from the
literature we demonstrate the relevance of our findings for the interpretation
of the Kerr effect measurements in superconductors.
