Towards the end of the last glaciation, ice sourced from the western Grampian Mountains of Scotland flowed down Strath Spey to encroach on the northern flanks of the Cairngorm Mountains. The maximum of this late advance and its subsequent retreat is recorded by moraines, ice-marginal meltwater channels, and kame terraces that can be traced for 60 km along Strath Spey. New cosmogenic 10Be exposure ages from moraines indicate deglaciation at 15.1 ± 1.1 ka. This timing matches closely the recalibrated mean ages of 14.7 ± 0.7 and 15.2 ± 0.7 ka for the Wester Ross Readvance in the North-West Highlands. A synchronous readvance of the British–Irish Ice Sheet (BIIS) towards the end of Greenland Stadial 2a (GS-2a) (16.9–14.7 ka) is indicated. Thereafter active ice retreat from the flanks of Strath Spey was rapid, occurring within the ∼1 ka uncertainty of the cosmogenic exposure ages. We suggest the advance followed the collapse of the marine parts of the BIIS at ∼16 ka due to conditions of increased precipitation occurring at a time of low temperatures. The rapidity of deglaciation may reflect enhanced Föhn effects caused by the ice dome in the western Grampians.