  The Gerasimov-Drell-Hearn and Baldin-Lapidus sum rules are evaluated in the
dressed K-matrix model for photon-induced reactions on the nucleon. For the
first time the sum $\alpha+\beta$ of the electric and magnetic polarisabilities
and the forward spin polarisability $\gamma_0$ are explicitly calculated in two
alternative ways -- from the sum rules and from the low-energy expansion of the
real Compton scattering amplitude -- within the {\em same} framework. The two
methods yield compatible values for $\alpha+\beta$ but differ somewhat for
$\gamma_0$. Consistency between the two ways of determining the
polarisabilities is a measure of the extent to which basic symmetries of the
model are obeyed.
