Seismic reflection events from recently acquired profiles in southern England are interpreted in terms of stratigraphic and structural interfaces between rock units. In particular, evidence is brought forward that a series of reflection events, dipping between 22° and 27°, with azimuth averaging 160°, represents 2 major thrust zones occurring in the Variscan floor beneath Mesozoic cover. A geological model based upon borehole information and regional geological considerations is presented. The tentative recognition of crystalline basement overlain and overstepped by late Proterozoic rocks of variable thickness suggests that basement in this area was unstable from late Precambrian times. The Mesozoic structural evolution can be related to tectonic re-activation of major concealed thrust zones in the Palaeozoic 'basement'.