  In a series of recent papers, it has been proposed that high field magnetic
white dwarfs are the result of close binary interaction and merging. Population
synthesis calculations have shown that the origin of isolated highly magnetic
white dwarfs is consistent with the stellar merging hypothesis. In this
picture, the observed fields are caused by an alpha-Omega dynamo driven by
differential rotation. The strongest fields arise when the differential
rotation equals the critical break-up velocity and result from the merging of
two stars (one of which has a degenerate core) during common envelope evolution
or from the merging of two white dwarfs. We now synthesise a population of
binary systems to investigate the hypothesis that the magnetic fields in the
magnetic cataclysmic variables also originate during stellar interaction in the
common envelope phase. Those systems that emerge from common envelope more
tightly bound form the cataclysmic variables with the strongest magnetic
fields. We vary the common envelope efficiency parameter and compare the
results of our population syntheses with observations of magnetic cataclysmic
variables. We find that common envelope interaction can explain the observed
characteristics of these magnetic systems if the envelope ejection efficiency
is low.
