A spectral method for modelling of tides is proposed and applied to the calculation of the M2 component of the tide in the English Channel. The classical non-linear hyperbolic problem of long wave propagation in shallow waters is transformed into a sequence of elliptic problems by looking at a multiperiodic solution the frequencies of which are previously known. The method is based upon a perturbation technique, but the principal difficulties arise from the non-analytical form of the quadratic friction term: the main conclusions of the corresponding study only are given here, because the purpose of this paper is to present a practical application of the method to the calculation of a tidal component by the finite element method. The variational formulation of the problem is presented, and the finite element package used is described. Some results are given for the M2 tide in the English Channel: cotidal maps and current fields.