A multidisciplinary investigation was undertaken to establish the palaeoecology of three different fluvial depositional environments in the basal sediments of a richly fossiliferous channel infill at Whittlesey, eastern England, which is dated by amino acid racemization (AAR) to marine oxygen isotope stage (MIS) 7. Molluscan and coleopteran data indicate that the river flowed throughout the year, supporting extensive adjacent marshland. Palaeobotanical and insect evidence indicates that extensive deciduous woodland was present, and the ostracod evidence indicates that saline habitats were available locally, suggesting that sea level at the time was not much different to today. Pollen and insect data do not differentiate the three different depositional environments, in contrast to the molluscan and ostracod evidence. Temperature estimates based on insect and ostracod data indicate a ‘mutual mutual’ mean July temperature of 16–21 °C and −1 to 3 °C for January. This is the first fully interglacial fluvial fossil assemblage described so far for the River Nene catchment that is reliably dated to MIS 7. Of particular note is the molluscan assemblage, which contains eight exotic species, including Theodoxus danubialis – a species described previously in the United Kingdom only in MIS 11 deposits associated with the River Thames catchment. Also of note is the insect assemblage, which in contrast contains no exotic species – unlike other MIS 7 insect assemblages recorded so far in the United Kingdom. Together these faunal assemblages may suggest a hitherto uninvestigated phase of a British interglacial stage, which the AAR data indicate could be late in MIS 7. The possibility that this so far unique interglacial fossil assemblage is the result of a combination of local preservation potential and environmental factors, however, cannot be ruled out.