New geomorphological and sedimentological data support previously published reconstructions of an Irish Sea Glacier advance as far south as the northern shores of the Isles of Scilly in the Celtic Sea (49°58'N). Offshore, boulder-covered bars with cores of diamicton are interpreted as moraines, which together with onshore moraine ridges and trimlines mark the maximal extent of the Irish Sea Glacier. At Bread and Cheese Cove, St. Martin's, a heterogeneous sediment unit, wedged between periglacial gelifluctates, is interpreted as a mixture of glacitectonized and cannibalized glacilacustrine and marine deposits as well as primary subglacial tills. Macrofabric signatures reflect a subglacial origin, but the whole unit has been subject to down-slope mass movement. Micromorphological analysis indicates highly variable response to deformation and glacitectonism, with most features relating to ductile behaviour and wet deformation. The characteristics suggest deposition during a short-lived advance of the Irish Sea Glacier over pre-existing marine and contemporaneous proglacial lacustrine sediments. Once blocks of stratified sediment and diamicton had been driven onshore, they were subject to paraglacial remobilization, resulting at most locations in complete disaggregation. The distribution of re-worked glacigenic sediments coincides with the glacial limits inferred from the geomorphological evidence.