Excavations in 2008 on the site of a proposed new prison at Belmarsh West, London Borough of Greenwich, found the heavily decayed remains of two superimposed Early Neolithic trackways. These structures, which are radiocarbon dated to the first quarter of the 4th millennium cal BC comprise some of the earliest structures yet encountered in the London Basin. The trackways were found towards the base of a peat sequence, immediately above the underlying Devensian gravels. The associated palaeoenvironmental record suggests that they were constructed in response to rising base levels, within a local floodplain environment dominated by alder carr, in order to maintain mobility across an expanding wetland landscape. The archaeological and geomorphological background to the excavations and a description of the results of the excavations are presented, with a particular emphasis on the Neolithic structures. The significance and wider context of the structures are examined through a consideration of their construction, wider palaeoenvironmental context, and the ways in which the structures can shed light on the nature of Early Neolithic subsistence strategies and land-use within the Thames floodplain.