The Maryport fault forms part of the faulted southern margin of the Northumberland-Solway Basin. Seismic reflection data reveal a complex history of repeated fault reactivation. Large oblique-normal displacements on the fault controlled early Carboniferous extensional basin development. Subsequently, Variscan basin inversion was accompanied by partial reversal of the fault. In Permian and Mesozoic times, renewed oblique-normal displacements strongly influenced basin subsidence. Further partial reverse displacement occurred as the Solway Basin was again inverted, probably in mid-Tertiary times in response to Alpine compression. The Maryport fault is most unusual, therefore, in providing direct evidence of the principal post-Caledonian tectonic events in southern Britain.