In 1430 Angus was sent on embassy to England as one of the commissioners to negotiate an extension of the truce with the newly crowned Henry VI of England which was prolonged for five years. Later in that year he was appointed Warden of the Middle March. In 1435 Angus led a troop of men to invest Dunbar Castle. The castellan, George II, Earl of March, had previously been made a ward of the King, and the garrison surrendered the castle bloodlessly.