Reflection seismic records from the Western Approaches Basin (SW UK Continental Shelf) reveal SSE-dipping reflection packages within the Variscan basement. These have been mapped and are believed to originate from Variscan thrusts. Orthogonal transfer faults are apparent as NNW-trending zones of discontinuity. Structural trends in the Permian-Mesozoic Western Approaches Basin parallel those of the underlying basement. An end-Variscan structural high in the northern part of the basin was progressively onlapped from the south during Permian times. This high may have been formed by thrust-driven tectonic thickening of the crust. During Late Jurassic-Early Cretaceous times Variscan thrusts were reactivated in the western part of the basin (Melville Basin) to form a half-graben. However, in the east (St Mary's Basin), the basin is more symmetrical, and Mesozoic reactivation of Variscan thrusts cannot be unequivocally demonstrated.