the history behind the story
The history of how the Windrush Poles came to be on the ship in 1948 began around a decade earlier, in what was then eastern Poland.
Map showing Polish territory as at 1933. Reproduced with the kind permission of the United States Holocaust Memorial Museum.
In the impending shadow of WW2, Germany under Adolf Hitler and the Soviet Union under Joseph Stalin signed a secret pact in which they agreed that they would not attack each other and that they would carve up Poland between them. This was the Molotov-Ribbentrop Pact, signed on 23 August 1939.
On 1 September 1939, Hitler invaded Poland from the west, and on 17 September 1939 the Soviet Union invaded Poland from the east. They met at what was known as the Curzon Line, a boundary that had first been proposed during the Polish–Soviet War of 1919–20. 
After the invasion, Poland had effectively ceased to exist as a separate country. The reality for the Poles living in the east of what was formerly Poland, was that they were now on land controlled by Russian forces.
Map showing Polish territory after the Molotov-Ribbentrop Pact 1939. Reproduced with the kind permission of the United States Holocaust Memorial Museum.
The western part of Poland had been taken over by Germany and so the Polish Government now had no safe place from which to govern. Its members fled to France and subsequently to England, becoming a government-in-exile.
Stalin conducted mass deportations of Polish nationals to the Soviet Union, including Kazakhstan and Siberia, in February, April and June 1940 and June 1941.
Approximately 1.5 million Poles were taken in this way. They were placed in unheated cattle trucks with no food and sent over 1,000 miles to forced labour camps and collectives. There they had to live in primitive conditions and do hard manual work in exchange for basic subsistence. For those in Siberia the temperatures were sub zero for months of the year, and could plummet to -50°C in winter.
However, this situation was to change. On 22 June 1941 Germany invaded the Soviet Union in Operation Barbarossa. Hitler was no longer honouring the Molotov-Ribbentrop Pact; he had become Stalin’s enemy. German forces swept eastwards, taking over the Polish territory that the Soviet Union had acquired under the pact.
General Władysław Sikorski, Commander-in-Chief of the Polish Army and Prime Minister of the Polish Government-in-Exile, took advantage of the situation to persuade Stalin to release the Poles from the labour camps. He proposed that the Poles would be able to assist Stalin in fighting the Nazis.
Reluctantly, Stalin agreed to what he called an ‘amnesty’ for the Poles in the camps, on condition that those who could fight would join a newly formed army led by Polish General Władysław Anders.
Stalin did nothing to help the departing refugees, and in many cases, they were hindered from leaving. Those Poles who did manage to go had to make their way across the vast Soviet Union to assembly points, from where they went on to Iran. In some cases this meant a total journey of over 2,000 miles. So brutal had their living conditions been and so difficult was the journey they now had to make, that many Poles died of exhaustion and malnutrition. Fewer than 10 per cent of those who had been taken from their homes in Poland successfully made that journey out of Soviet Russia.
Anders' Army was then sent to the Middle East, where it operated under British command. The civilians were dispersed to camps all over the world for the rest of the War.
US President Franklin D. Roosevelt, British Prime Minister Winston Churchill and Soviet Premier Joseph Stalin met at three conferences held during and after the war, at which they discussed the boundaries of Poland. These were the Tehran, Yalta and Potsdam Conferences. The outcome of these was that the Soviet Union would permanently retain land to the east of Poland. 
This meant for many Poles that even after the War had ended, they could not return home, as they would be under the occupying communist regime, unlikely to regain their lost land and in danger of persecution.
The Poles who had fought for the Polish Free Forces supporting the Allies were eventually given the right to bring their relatives to England under the Polish Resettlement Act 1947. Those who took this up were placed in camps, later gradually integrating into British society. Those who did not, found permanent homes in other countries.
In May 2017 the Polish Government estimated that there were 18–20 million Poles now living outside the borders of their own country.  This Polish diaspora is one of the biggest in the world.
© Jane Raca 2023
[2 ]God’s Playground, Professor Norman Davies page 364-5.
 Embassy of the Polish Republic in London: http://london.mfa.gov.pl/en/news/day_of_the_polish_diaspora_and_poles_abroad