The constitutional annexation of Wales to England, begun under Edward I and completed by Henry VIII, extended the respective powers of king and parliament first over parts and finally over the whole of the country. In the ‘act of union’ of 1536 what was proposed was a parliamentary arrangement of laws and justice, an enlargement of the Edwardian settlement designed for all Welsh lands. The historic principality – the territory ruled over by the Welsh princes of Gwynedd until the conquest of 1282 and since 1301 reserved for the eldest sons and heirs of the kings of England – appeared to have been extinguished in the Tudor ‘union’. In 1543 the ‘second act of union’ of Henry's reign (as it is known in modern Welsh historical accounts) contained a proviso which tempered the parliamentary union of laws previously proposed by reaffirming the royal powers to legislate for Wales that Edward I had originally assumed in 1284. This proviso supplies a key to the constitutional relationship of crown and principality over the previous two and a half centuries. Neither that relationship nor the proviso itself has always been well understood, and it was an anachronistic reading of the latter that led to its repeal in 1624. The original legislative intention in 1543 was to be subjected to conflicting interpretations in James Ps reign by those who sought to identify the historical nature of the principality and the crown's prerogative in Wales in order to define their present extent and future potential.