Another case in which the Cabinet enjoyed more than formal powers over a foreign policy decision was that of entry into the war itself, a choice faced directly during the two days following the German invasion of Poland on 1 September, and after weeks of anticipation and increasing tension. This climacteric has understandably attracted a good deal of attention from historians, and there is no need to rehearse its details at length here. However the events of 1–3 September provide dramatic material for the student of Cabinet decision-making, particularly in conditions of crisis, for they included one of the plainest Cabinet ‘diktats’ in British political history.

This was a very different type of decision from those which preoccupied ministers during the Soviet negotiations. Most obviously, the time-span of deliberation was very short at less than forty-eight hours. In one sense the urgency was self-imposed. Hitler had sent no ultimatum to Chamberlain or Daladier. At bottom, however, circumstances were dictating rapid action. The arrival at 7.28 a.m. on 1 September of a Reuters report of Hitler's broadcast announcing war with Poland raised the question of whether the casus foederis of the March Guarantee had finally arrived. His Majesty's Government were confronted with an unavoidable choice between war with Germany and the abandonment of their new policy of support for the vulnerable states of eastern Europe. The middle way, of negotiations on the basis of a status quo ante, was hardly realistic.