The problem of Anglo-Soviet relations in the later spring and summer of 1939 usefully provides both a parallel and a contrast to that of the Polish Guarantee. It was of equally vital importance to British foreign policy, both objectively and increasingly in terms of the way it was perceived by participants. Its outcomes, whatever they might be, would inevitably affect the military and political balance in Europe, since it involved the consideration of advance commitments to go to war. It was also seen as a pressing issue, although slightly less so than the events of March. Ministers rapidly recognised in April that continued German expansionism meant that relations between Britain and the USSR could no longer remain ill-defined. An immediate attempt to reach some kind of agreement had to be made. However, in contrast to the guarantee to Poland, the salience of this problem did not deeply disturb the central notions of British policy-makers about European politics. For it arose gradually out of the deliberations about Poland, and it was not a new or sudden trauma of itself. Indeed to some extent it was left-over business from those last two hectic weeks of March. Once the invasion of Prague had been assimilated, and the guarantee issued to Poland, the idea of concluding a full alliance with the USSR was not so radical as it would have seemed even six months previously. Moreover the proposals that emerged were formal, detailed and multifaceted. Both procedurally and substantively the contrasts and similarities between the March crisis and the Soviet negotiations throw interesting light on the relationship between policy-making and the problems with which it deals.