Once Britain had become separated from the European mainland in the seventh millennium BC, Mesolithic stone tool traditions on opposite sides of the newly formed Channel embarked upon different directions of development. Patterns of cross-Channel contact have been difficult to decipher in this material, prior to the expansion of farming (and possibly farmers) from northern France at the beginning of the fourth millennium BC. Hence the discovery of Late Mesolithic microliths of apparently Belgian affinity at the western extremity of southern Britain—in the Isles of Scilly—comes as something of a surprise. The find is described here in detail, along with alternative scenarios that might explain it. The article is followed by a series of comments, with a closing reply from the authors.