Middle Pleistocene fluvial deposits of the Corbets Tey Formation at Purfleet, Essex, provide evidence of an un-named and previously poorly recognized interglacial, thought to corrrelate with Oxygen Isotope Stage (OIS) 9. Previous attributions of the sediments to the Ipswichian (Last Interglacial) Stage are refuted. New investigations have yielded rich molluscan, mammalian and ostracod assemblages that indicate fully temperate conditions and the distal influence of marine transgression. Pollen analyses suggest a previously unrecorded phase of interglacial vegetational development. Clast composition, geomorphological evidence and the occurrence of molluscs that favour large rivers all point to deposition by the Thames, rather than in a minor tributary, as suggested previously. Three separate Palaeolithic industries in stratigraphical superposition are recognized at Purfleet, these being Clactonian, Acheulean and Levallois. Purfleet is therefore a key locality in the understanding of the early human occupation and exploitation of southern Britain, as well as for the interpretation and correlation of the terrace sequence in the Thames Valley