How did the various currents of the British left respond to two competing nationalisms seeking to found a state in Palestine? The Labour Party from 1917 onwards helped to popularise the Zionist project as a social democratic experiment that would bring progress to the Middle East. The party’s colonial experts largely ignored the sectarian practices of the Labour Zionist movement, which through its trade union and kibbutzim, sought to build an exclusively Jewish economy. The British Communist party alone provided a critique of Labour Zionism but in 1947 in line with the Soviet Union’s Middle East policy it reversed its position. Over the following two decades the left was overwhelmingly supportive of the Israeli state considering its establishment as a recompense to the Jewish people for the Holocaust. The left-wing Zionist party, Poale Zion played an important role as intermediary between, on the one hand, the British labour movement and, on the other, Anglo-Jewry and the Israeli Labour Party. By contrast, there was no significant political force in Britain to represent the Arab nationalist viewpoint. The destruction of Palestinian society in the 1948 war and the refugee crisis resulting from it barely registered in Western public consciousness. It was not until the rise of the new left in the late 1960s, that Palestinian nationalist aspirations found a voice on the British left and began to command mainstream attention. After highlighting the major shifts in the left’s appraisal of Israel and Zionism, this study examines the argument that its pro-Palestinian sympathy stems from antisemitism.