Many migrants were seeking safety from persecution:
-December 1938 - September 1939 over 8,000 Jewish children came (Kindertransport)
Many migrants were looking for work as after WW2 people were needed to help rebuild due to bombing
People from colonies (especially Caribbean) were encouraged as there were not enough European migrants. They then helped with rebuilding and took jobs in TFL and NHS. A specific example of this was the Windrush in 1948 (under the British Nationality Act)