The second half of the European Middle Pleistocene (MIS 10-8) witness the end of Lower Palaeolithic, while technical innovations specific to the Middle Palaeolithic already emerge sporadically. An increasing systematisation and predetermination of small blank debitage are at the heart of this turning point, but methods of large flake (>10 cm) production involving varying degrees of prediction and/or predetermination are also attested at this time. The study of large flake debitage could therefore help to better characterise the variability of this period technical systems, and question their potential involvement in the technical trajectories that led to the Middle Palaeolithic. Although large flake industries are mainly concentrated in the Southwest of the continent, Menez-Dregan I sea cave in the Armorican Massif stands out as an exception. A new techno-economic study of the most recent occupational level in the sequence (4ab; MIS 9-8) confirms the presence of large products during this pivotal period in the region, either without further working, or used as tools and/or core blanks. The raw materials of coarse-grained rocks such as sandstones, quartzites and microgranites, come exclusively from pebble beaches accessible nearby. The flakes are mainly neocortical first removals, but sometimes have one or more removals prior to debitage. The acquisition techniques and methods are still difficult to characterise and do not seem to match any classic debitage patterns for this period. A technopetrographic experimental approach focusing on the impact of available raw materials on technical choices provides new insights into the place of this large-scale debitage practice within the Menez-Dregan atypical technical system in Northen Europe.