Millennial-scale variability in the flux of ice-rafted detritus to North Atlantic sediments during the last glacial period has been interpreted to reflect a climate-forced increase in the discharge of icebergs from ice-sheet margins surrounding the northern North Atlantic Ocean . But the relationship between ice-sheet variability and climate change is not clear, as both the sources of ice-rafted detritus and the ice-marginal processes are varied and complex [2-4]. Terrestrial records are helpful in unravelling this complexity because they can demonstrate the scale of ice-sheet oscillations, and whether the ice sheet (or sector) was advancing or retreating with respect to climate change. Here we constrain the age and anatomy of a prominent readvance of the British Ice Sheet in the northern Irish Sea region at [approximately] 1414 C kyr BP ([approximately] 16.4 calendar kyr BP). The analysis indicates that the British Ice Sheet participated in an iceberg discharge episode known as Heinrich event 1. Comparison with other terrestrial and marine ice-sheet records suggests that the dynamic collapse of the Laurentide Ice Sheet beginning at 14.6-15.014 C kyr BP [1,4] ([approximately] 17.2-17.6 calendar kyr BP)  initiated varied responses from other ice-sheet margins around the northern North Atlantic region. These observations support the argument that the release of icebergs and meltwater during Heinrich event 1 disrupted the North Atlantic thermohaline circulation [6-8], leading to a delay or reversal of deglaciation of the Northern Hemisphere and at least as far south as 40 degrees S for two to three thousand years [5,9,10], suggesting a climate forcing and response similar to that of the ensuing Younger Dryas 'cold snap' [11,12].