A semiclassical, internally consistent formulation of the dipole polarisabilities of atoms, of the shell model of ionic crystals, of the induced electric field effects on oscillator strengths in atoms and of the induced valence electron effects on the electronic energy levels was presented and applied to atomic lithium in earlier works and is applied to the remaining alkali atoms: sodium, potassium, rubidium and caesium. The results indicate that the simple induced dipole potential of the core due to the presence of the valence electron accounts for the major portion of the correlation effects to be added to a Hartree-Fock calculation in the alkali atoms. The model applies well to non-relativistic quantities. However, there are indications that the simple one-particle approximation is inaccurate for relativistic corrections.