 During the same year, when the Labour Government's parliamentary majority was under threat, he threatened to resign unless the far-left in his constituency party were brought under control.Following pressure from the far-left in his local party, O'Halloran was among the Labour MPs who defected to the newly founded Social Democratic Party (SDP) in 1981.However, in 1983, the SDP chose John Grant, the MP for Islington Central (which was being abolished in boundary changes), to be their official candidate in Islington North.