The War gave Labour an opportunity for influence greater than it had had since 1931 – and one which it now used with striking effectiveness. The collapse of the Chamberlain Government in May 1940 was brought about partly because of a growing disaffection on the Tory backbenches–but also as a result of a collective Labour determination not to be bought off. In all parties, a broad ‘national’ coalition was regarded as desirable, if not essential. By indicating their willingness to serve in such a government, but only if Chamberlain was not at the head of it, Labour leaders were able to exert a crucial pressure. Meanwhile the Nazi – Soviet pact removed, at a stroke, one factor which had hitherto stood in the way of Parliamentary alliances. Soviet ‘benevolent neutrality’ towards Germany after August 1939 shattered the far left in Britain, and the Popular Front ceased to exist as a symbolic and divisive issue.

After the publication of Cripps' ‘Memorandum’, there were no further serious attempts by Labour leaders to coordinate activities with other opponents of the Government before War was declared. One reason was the Petition Campaign. Another was Labour's uncertainty about military service. Early in 1939, the Churchill and Eden groups increased pressure on the Government to accept conscription. Labour remained opposed to any form of compulsory military service. At the end of March, Churchill, Eden, Cooper and other Tories signed a motion calling for a National Government ‘on the widest possible basis’, and linked this to military and industrial conscription. At the end of April, the Government introduced a limited form of compulsory National Service. The PLP and most Liberals opposed.