  We continue our study of non-Abelian gauge theories in the framework of
Epstein-Glaser approach to renormalisation theory. We consider the case when
massive spin-one Bosons are present into the theory and we modify appropriately
the analysis of the origin of gauge invariance performed in a preceding paper
in the case of null-mass spin-one Bosons. Then we are able to extend a result
of D\"utsch and Scharf concerning the uniqueness of the standard model
consistent with renormalisation theory. In fact we consider the most general
case i.e. the consistent interaction of $r$ spin-one Bosons and we do not
impose any restriction on the gauge group and the mass spectrum of the theory.
We show that, beside the natural emergence of a group structure (like in the
massless case) we obtain, new conditions of group-theoretical nature, namely
the existence of a certain representation of the gauge group associated to the
Higgs fields. Some other mass relations connecting the structure constants of
the gauge group and the masses of the Bosons emerge naturally. The proof is
done using Epstein-Glaser approach to renormalisation theory.
