  Precision flavour observables play an important role in the interpretation of
results at the LHC in terms of models of new physics. We present the result for
the one-loop Z penguin in generic extensions of the standard model which
exhibit exact perturbative unitarity. We use Slavnov-Taylor identities to study
the implications of unitarity on the renormalisation of the Z penguin, and
derive a manifestly finite result that depends on a reduced set of physical
couplings.
