Dear edskarf,
Thank you so much. You are absolutely right, I had completely forgotton about the white stripes between the red ones on the rudder. After I got my PPL I went on to fly that very same Auster too, G-AJUO in August 1959. And I am sure the instructor in the video is Yvonne Pope, she taught me, went on to be an ATCO and ended her career as a captain in Dan Air.
Once again, many thanks.