New apatite fission-track analyses from NW Britain indicate that a maximum of 2.5 km of erosion has occurred there during the Cenozoic, similar to values for SE Greenland and the east Greenland coast north of Scoresby Sund. The erosion may have been facilitated by magmatic underplating during break-up. However, at Kangerdlugssuaq, East Greenland, 4–6 km of erosion is measured since 45 Ma. Lower–mid-Eocene marine sedimentary rocks overlying the lavas on the Blosseville Coast indicate that magmatic underplating on the central Greenland coast substantially post-dated flood volcanism and break-up, behaviour not predicted by simple plume-rift models. Subsidence reconstructions of the Hebrides Shelf, and the east and west Greenland coasts, show that rapid, dynamic uplift was effectively synchronous at 63 Ma and preceded volcanism by <1.6 million years. The magnitude of uplift on the Hebrides Shelf (c. 400 m) is compatible with a mantle temperature anomaly of c. 100°C. These data suggest very rapid lateral flow of the impacting Iceland plume head. The predicted crossing of the plume by the east Greenland coast in the mid–late Eocene would account for post-rift magmatic underplating and dynamic support on the Greenland but not the European side of the North Atlantic basin.