The identification of extensive intrusive igneous complexes in both subsurface data and field studies has led to the quantification of the volumes of igneous material present within sedimentary sequences. Despite this research, however, little connection has been established between the amount of igneous material intruded into a basin and its effect on subsequent basin evolution in terms of burial and loading. We used subsurface data from the Faroe–Shetland Basin to investigate igneous intrusions with the aim of understanding how additional igneous material influences basin evolution. We found that the total estimated thickness of Cretaceous sediments is likely to be an overestimate because the sedimentary fill consists of significant quantities of igneous material emplaced during the Paleocene (56–54 Ma). This additional igneous material has not previously been accounted for in estimates of sedimentation rates and the burial history of the Faroe–Shetland Basin. Petroleum system modelling to understand the generation and expulsion of hydrocarbons benefits from correct estimates of basin fill. The overthickening of basins by igneous material will affect the timing of hydrocarbon generation and therefore the correct evaluation of exploration targets. The volume of igneous material and the time at which this material was emplaced must be acknowledged and considered in order to fully understand basin evolution.