Establishment
Divisions appeared in the new organisation almost immediately. The Derry Journal, generally sympathetic to the nationalist cause, attacked two prominent members: T. J. Campbell for resigning as an MP in order to take up a position as a judge, and Cahir Healy for pledging to support the Ulster Unionist Party leadership of the Parliament in their campaign to withhold some Imperial Contributions in order to improve housing. A few months later, Thomas Maguire accused McSparran of rejecting a position as a judge solely because it was insufficiently well paid.
In 1946, Sean O'Gallagher was appointed as full-time organiser for the League, and by the end of the year, forty local Anti-Partition clubs linked to the League had been established. In July, Gerry Lennon, McAteer and McSparran spoke at a rally in Birmingham in July to launch a British section of the League. In Britain, the group tried to work with Labour Friends of Ireland, but were frustrated as the group de-prioritised the question of partition. The two organisations did draw up a joint amendment to the Northern Ireland Bill calling for a full discussion on the governance of Northern Ireland.
The League held its first annual convention at Dungannon on 11 April 1947. 146 delegates attended, nominated by 63 branches, and McAteer was elected Vice Chairman. The following year, it opened an office in Belfast. It faced its first electoral test at the Armagh by-election, 1948, nominating James O'Reilly. O'Reilly failed to gain the Unionist-held seat, but took 40.3% of the vote.
Read more about this topic: Irish Anti-Partition League