This paper explores the estimation of river flood frequencies by modelling catchment runoff on a continuous time basis. The work uses the modelling of a sample of British catchments as a basis for generalization in space, such that ungauged sites can potentially be addressed by the method. The principles of the method are outlined. Pilot study hood frequency results for site-specific and for spatially generalized model parameter estimation are discussed. Examples are given of an extension of the method in time to allow estimates to be made of high recurrence interval floods, and of the ability of the method to incorporate changed climatic regimes.