In 1819 the Seminary faced a legal challenge from the British governor of the province to its holding of various seigneuries in Quebec, which were its primary means of support. Lartigue was entrusted with the superior of the Seminary with a mission to London to present their case directly to the government in England. The superior chose Lartigue as being particularly qualified for the mission because of his knowledge of the law and his mastery of English. For this he was to accompany Bishop Plessis, who was traveling there to secure letters patent for the establishment of a new seminary and for permission to divide the Diocese of Quebec, which was proving unmanageable. They sailed for London on 3 July 1819 on the "George Symes", arriving on 14 August.