This is Christopher Morris's arrangement of the Prelude to the 1941 film, The 49th Parallel (called The Invaders in the US). The piece is also known as The New Commonwealth after words were written to fit it.
I thought twice about recording and uploading it, partly because the original orchestral version is so much better, but also because of the vexed question with this piece of tempo. I initially paced it a lot faster than this, given the direction "Andante sostenuto", but when I listened to online performances, they varied enormously (one goes to 3' 23"!) but were all much slower, and, to my mind, gave it a grandeur which was missing at my speed.