Abstract Ormesby Clay Formation mudstones in eastern Norfolk are the oldest upper Paleocene deposits (Chron C26r) of southern England. The base of the type Thanet Sand Formation (= start of the Thanetian Stage) is approximately 0.65 my younger (C26n). C25n is missing from the stratigraphic record across much of southern England indicating an hiatus >0.5 my between the Ormesby Clay-Thanet Sand Formations and the Lambeth Group. However, in Central London the basal unit of the Lambeth Group, the Upnor Formation, contains a record of C25n. The bulk of the Lambeth Group, the Harwich Formation and lower London Clay Formation, were all deposited during Chron C24r. The NP9/10 boundary, a commonly used Paleocene/Eocene boundary marker, is correlated with the unconformity (approximately 0.4 my) that separates the Lambeth Group from the Harwich Formation. The start of C24n.3n is positioned at the base of Division B of the London Clay and leper Clay Formations. In the Hampshire Basin, an unconformity of at least 0.66 my is marked by the absence of a record of Chron C22n.