So this is where the Speedbird logo of British Airways comes from. The sculpture is called Speed Wings over the World and it is by Eric Broadbent, who seems to be known mainly just for this work.
The building, now the National Audit Office, was built to the designs of Albert Lakeman in 1937/9. It was strategically located next to Victoria Station so passengers, mail and cargo could be loaded onto trains and sent to Southampton where they were transferred to the flying boats that took them to India, Australia and Africa. Of course, you didn't need a passport then because it was all British.
The title is a bit ambitious - at the time it took nearly a month to get to Australia. Planes used to land for overnight stops that were excuses for taking tours, shopping and dining on a heroic scale.
After the war, Imperial Airways was merged with British Airways, the then European carrier, to form BOAC. It used the terminal until the 1970s.