  In this paper a complete generalisation of the Catani-Seymour dipole
subtraction method to next-to-leading order electroweak calculations is
presented. All singularities due to photon and gluon radiation off both
massless and massive partons in the presence of both massless and massive
spectators are accounted for. Particular attention is paid to the simultaneous
subtraction of singularities of both QCD and electroweak origin which are
present in the next-to-leading order corrections to processes with more than
one perturbative order contributing at Born level. Similarly, embedding
non-dipole-like photon splittings in the dipole subtraction scheme discussed.
The implementation of the formulated subtraction scheme in the framework of the
Sherpa Monte-Carlo event generator is detailed and numerous internal
consistency checks validating the obtained results are presented.
