  A complete family of non-expanding impulsive waves in spacetimes which are
the direct product of two 2-spaces of constant curvature is presented. In
addition to previously investigated impulses in Minkowski, (anti-)Nariai and
Bertotti-Robinson universes, a new explicit class of impulsive waves which
propagate in the exceptional electrovac Plebanski-Hacyan spacetimes with a
cosmological constant Lambda is constructed. In particular, pure gravitational
waves generated by null particles with an arbitrary multipole structure are
described. The metrics are impulsive members of a more general family of the
Kundt spacetimes of type II. The well-known pp-waves are recovered for
Lambda=0.
