Answer :
The reaction of France and Britain to the Soviet invasion and annexation of Eastern Poland was muted, since neither country expected or wanted a confrontation with the Soviet Union at that time. Under the terms of the Polish-British Common Defence Pact of August 25th, 1939, the British had promised assistance if a European power attacked Poland. A secret protocol of the pact, however, specified that the European power referred to Germany. When Polish Ambassador Edward Raczyński reminded Foreign Secretary Lord Halifax of the pact, he was bluntly told that it was Britain's business whether to declare war on the Soviet Union. British Prime Minister Neville Chamberlain considered making a public commitment to restore the Polish state but in the end issued only general condemnations. This stance represented Britain's attempt at balance: its security interests included trade with the Soviets that would support its war effort and the possibility of a future Anglo-Soviet alliance against Germany. Public opinion in Britain was divided between expressions of outrage at the invasion and a perception that Soviet claims to the region were reasonable.
side note: I found this information with this link, https://en.wikipedia.org/wiki/Soviet_invasion_of_Poland