  We present a simple proof of the absence of Bose--Einstein condensation of a
relativistic boson gas, in any finite local magnetic field in less than five
dimensions. We show that the relativistic charged boson gas exhibit a genuine
Meissner--Ochsenfeld effect of the Schafroth form at fixed supercritical
density. As in the well--known non--relativistic case, this total expulsion of
a magnetic field is caused by the condensation of the Bose gas at vanishing
magnetic field. The result is discussed in the context of kaon condensation in
neutron stars.
