The United Kingdom and Poland form a military alliance in which the UK promises to defend Poland in case of invasion by a foreign power.

The Second Polish Republic, at the time officially known as the Republic of Poland, was a country in Central and Eastern Europe that existed between 7 October 1918 and 6 October 1939. The state was established in the final stage of World War I. The Second Republic was taken over in 1939, after it was invaded by Nazi Germany, the Soviet Union, and the Slovak Republic, marking the beginning of the European theatre of the Second World War. The Polish government-in-exile was established in Paris and later London after the fall of France in 1940.

The military alliance between the United Kingdom and Poland was formalised by the Anglo-Polish Agreement in 1939, with subsequent addenda of 1940 and 1944, for mutual assistance in case of a military invasion from Nazi Germany, as specified in a secret protocol.