The English successes in the 1410s–1420s after the revival of the Hundred Years war were not only due to their military supremacy but also to the deep political crisis in France which made it possible for the English king to be proclaimed heir to the French throne by the Treaty of Troyes (1420). In the 1420s the English claim to the French throne was able to attract support of some Frenchmen and bring them into the Lancastrian service. The paper looks at some of these so-called ‘faux françois’, the Frenchmen who were active in the service of the Lancastrian regime, exploring the routes which brought them into Lancastrian administration, the role played by them in the process of government and their destiny after the Treaty of Arras (1435) broke the Anglo-Burgundian alliance and effectively ruined any chances for the house of Lancaster to unite France under its rule.