New data from the complex Lower Thames locality at Purfleet, Essex, reinforce the correlation of interglacial deposits there with Marine Isotope Stage (MIS) 9, the second of four post-Anglian (MIS 12) interglacials recorded in the river-terrace sequence east of London. Arising from various developer-funded archaeologically driven projects, and primarily the construction of 'High Speed 1' (HS1: formerly the Channel Tunnel Rail Link), the new evidence includes additions to palaeontological knowledge of this interglacial, notably from ostracods and vertebrates, results from isotopic analyses of shell and concretionary carbonates, and the first application of numerical dating techniques at Purfleet. These analyses, combined with palaeotemperature estimates from the Mutual Ostracod Temperate Range method, confirm that deposition of the fossiliferous deposits coincided with interglacial conditions, with similar-to- or warmer-than-present summer temperatures and colder winters, providing a suggestion of greater continentality. OSL and amino-acid racemisation support correlation of the interglacial with MIS 9, whereas the climatic and sedimentological evidence points to correlation with the earliest and warmest substage (MIS 9e). There is also evidence that a greater part of the Purfleet sequence might date from the interglacial, although whether these also represent MIS 9e or later parts of the complex stage cannot be determined. The additional archaeological material is consistent with previous interpretations of a tripartite stratigraphical sequence of lithic traditions: basal Clactonian, above which is Acheulian (handaxe manufacture), followed by one of the earliest British appearances of Levallois technique. However, given the revised interpretation of the climatic affinity of the upper parts of the sequence, Levallois technique might have been used at Purfleet before the end of MIS 9.