During the final phase of the war the Spanish Republic's stubborn resistance was regularly punctuated by military and diplomatic defeats which denied it the hope of eventual success. Yet while the British public, perhaps predictably, sympathised with the Republic in its death agonies as never before, and rank-and-file solidarity in the labour movement reached ever higher levels, Spain's fate was less and less central to the attention of the leaders of British labour. This disjuncture led, in 1938, to sustained attempts to force both the Labour Party and the trade unions to take action to overturn Non-Intervention. The criticism of labour's policy which had previously been somewhat restrained, now became widespread within the movement.

Ironically, 1937 had ended on a note of optimism. Large Republican offensives were mounted in Aragon to deter Franco from attacking Madrid and the strategic city of Teruel was taken. Yet the celebrations were shortlived. Franco was not a general who lightly ceded territory and after bitter winter fighting all the Republican gains were lost. In lightning counteroffensives in the spring the rebel air supremacy was used to great effect in routing the People's Army. Franco's forces reached the sea at Vinaroz on 15 April 1938 and the Republic was split into two separate zones; Catalonia, now the seat of government, and a central zone inaccessible other than by increasingly hazardous sea routes.