  We investigate single top production in the presence of anomalous Wtb
couplings. We explicitly show that, if these couplings arise from gauge
invariant effective operators, the only relevant couplings for single top
production and decay are the usual gamma^mu and sigma^mu nu q_nu terms, where q
is the W boson momentum. This happens even in the single top production
processes where the Wtb interaction involves off-shell top and/or bottom
quarks. With this parameterisation for the Wtb vertex, we obtain expressions
for the dependence on anomalous couplings of the single top cross sections, for
(i) the t-channel process, performing a matching between tj and t bbar j
production, where j is a light jet; (ii) s-channel t bbar production; (iii)
associated tW- production, including the correction from tW- bbar. We use these
expressions to estimate, with a fast detector simulation, the simultaneous
limits which the measurement of single top cross sections at LHC will set on
V_tb and possible anomalous couplings. Finally, a combination with top decay
asymmetries and angular distributions is performed, showing how the limits can
be improved when the latter are included in a global fit to Wtb couplings.
