It's 'Mambo Vero' by the Heinz Schönberg Orchestra with the Dierene Singers - not sure what the original source was (possibly Delfina or Haifisch) but it was one of the tracks used on the BBC test card via Frank Chacksfield.
How the heck did you recognize that track??? Are you a connaisseur of Germany library music/German instrumental music by any chance? If yes, then I've got some more tracks to be identified here: https://www.youtube.com/channel/UClYsboUZXUJQ4-IAnzryOJQ/videos