Arthur was conceived in adultery and thus being illegitimate should not have acceded to the British throne. There were legitimate heirs to the throne, namely Modred and Gawain, sons of Uther's legitimate daughter, Morgause, by her marriage to Lot of Lothian and Orkney. However, through a misguided desire to have a king of their own people, the Britons chose Arthur instead. This is the version of Arthur's origins current in much late medieval Scottish historiography, and although various mitigating factors are offered to support the Britons’ choice, such as the youth of Lot's sons or Arthur's personal valour, Arthur's illegitimacy infects his behaviour. With the Scots particularly, he fails to keep his promises, so that ‘nor neuer stranger rang on ws nor had dominacioun of ws, Supposs Arthur þat tyrand maid weir on ws aganis his faith and promyss …’.

This quotation, from the Scottis Originale, highlights two essential features in this peculiarly Scottish approach: firstly, Arthur appears in the context of a statement regarding Scottish independence, and secondly he is immediately introduced as a ‘tyrand’. In English narratives, Geoffrey of Monmouth's pervasive presentation of Arthur as successful imperialist had been used to underpin English propaganda campaigns regarding their alleged sovereignty over the Scots as well as the rest of the British Isles. Therefore, in order to maintain the Scottish claim to independence, and to preserve their presentation of an unbroken line of sovereign kings lasting nearly a millennium, Scottish historiographers needed to undermine Arthurian claims. However, to omit Arthur and to ignore the Galfridian narrative altogether leaves rather too many holes in the chronological pattern. Rather than remove the hero completely, therefore, these accounts use Geoffrey's narrative, but challenge his conclusions, firstly by stressing the less salubrious aspects of Arthur's ancestry and secondly, in common with other English chroniclers, by denying Arthur's imperial success while acknowledging some of his success against the Saxons. What results is a curious mixture of praise and condemnation, evident in Latin chronicles from the fourteenth to the sixteenth century.