At hadron colliders, single top quarks can be produced via charged-current electroweak processes involving a Wtb vertex. A powerful prove studying this vertex comes from the measurement of the top-quark polarisation and the W-boson spin observables in the t-channel single top production. New physics effects resulting in corrections to the Wtb vertex would affect these observables. This talk reviews the latest published results by the ATLAS collaboration and the limits set to anomalous couplings of the Wtb vertex.