During his campaign to establish himself in Wales, Owain Glyndŵr wrote to the Scottish king seeking his support against a common enemy. On the surface Owain had an impeccable argument. The three sons of Brutus were the basis for a native British alliance against an alien invader, and Glyndŵr's letter provided a point of contact between Welsh and Scottish branches of the Arthurian heritage as depicted in Geoffrey of Monmouth's Historia Regum Britanniae. Unfortunately the letter never reached the Scottish king, and an opportunity for native British unity seemingly evaporated. However Glyndŵr's letter was not the only potential meeting of Welsh and Scottish interests in the political arena. Earlier, during the time of Edward I, later during the Wars of the Roses and again, at the beginning of the Stewart dynasty in England, circumstances brought them close together. Each time Geoffrey's view of history provided a means to articulate their relationships with one another, and Arthur as king of Britain provided a focus for defining identity and difference within the parameters of a British world.

After the Glyndŵr rebellion (1400–1415), the Welsh projected their Arthurian hopes onto Henry Tudor, ironically the founder of an essentially English dynasty, as the mab darogan (son of prophecy) who would restore the unity of Britain. These hopes transferred to his granddaughter Elizabeth I as the Protestant uchelwyr, that is, the gentry of Wales, found a wider political and economic role within the developing British nation. Geoffrey's Arthurian vision as a fulfilment of British destiny was sustained in poetry, particularly vaticination. Here it provided an important element in constructing the genealogies which linked gentry families to the ancient British kings of Geoffrey's world. During the sixteenth and seventeenth centuries, a number of historical treatises synthesised Geoffrey’s view of history, together with other traditional sources, in a way which favoured the existence of Arthur, and, by extension, the interests of the Welsh gentry. In Scotland, which had a different kind of political cohesion and independence, medieval and early modern chronicles linked Arthur more directly to issues of kingship and sovereignty. These chronicles were also aware of Arthur as a figure in romance and as a folk-hero. The attitude to Arthur in Scottish sources is often ambivalent, and there was, in addition, an alternative origin myth, the Scota story.