In 1968 the Public Records Office made available to historians British Cabinet papers relating to the years 1938 and 1939. This decision had renewed the debate on the extent of British responsibility for allowing Hitler to pursue his revisionist and aggressive policies in Europe. It has been asserted that the degree of British complicity, the logical consequences of appeasement, could be ascertained through the study of contemporary documents. The historical analysis of British involvement in the break up of Czechoslovakia has notably benefited from this development. It is therefore surprising to note that this has not been matched by an equally detailed analysis of the few months preceding the outbreak of the war, in particular the period from March till September 1939.

The assumption of an undertaking to aid Poland against German aggression on the 31 March has traditionally been seen as signalling a break in the foreign policy hitherto pursued by the British government. It is presumed, therefore, that the period from the end of March to the outbreak of the war is one of few new initiatives, in any case none which would contradict the assertion that in the closing days of March Britain had made a definite commitment to fight Germany.