A new high-resolution, c. 1 Ma mammalian record in continental Eocene–Oligocene strata in the Hampshire Basin is used to investigate the nature and timing of the major Europe-wide mammalian faunal turnover termed the Grande Coupure. Whether this was caused by climate change or by competition with taxa dispersing from Asia is controversial. The mammalian faunas in this record, after rarefaction analysis, show a sharp reduction in diversity only after the Grande Coupure. Improved correlation of NW European successions to global events confirms the Grande Coupure as earliest Oligocene. It shows that a c. 350 ka hiatus interrupts the Hampshire and Paris Basin sequences prior to the first record of post-Grande Coupure Asian taxa. Hiatus-bridging faunas from elsewhere in Europe record mainly post-Grande Coupure taxa, suggesting that the turnover occurred early in the hiatus, minimizing bias to the turnover pattern. A previously unrecorded, second, smaller turnover, involving European mammals only, immediately precedes the Grande Coupure in the Hampshire Basin, coinciding with vegetational change. This turnover is judged not to represent cooling. It is concluded that the Grande Coupure coincides with the earliest Oligocene Oi-1 glaciation and that climate change combined with competition to produce the turnover.