On 17 September, the Soviet Union invaded Poland through the eastern Polish border in keeping with the Molotov–Ribbentrop Pact's secret protocol specifying the division of Poland. According to the Polish-British Common Defence Pact, the United Kingdom should give Poland "all the support and assistance in its power" if Poland was "engaged in hostilities with a European Power in consequence of aggression by the latter". The Polish ambassador in London, Edward Bernard Raczyński, contacted the British Foreign Office to point out that clause 1(b) of the agreement, which concerned an "aggression by a European power" on Poland, should apply to the Soviet invasion. Halifax responded that the obligation of British government towards Poland that arose out of the Anglo-Polish Agreement was restricted to Germany, according to the first clause of the secret protocol.
