I can corroborate that it is not from the Beggar's Opera, it is from the play 'Die Rundkoepfe und die Spitzkoepfe', a Shakespeare adaptation first played in 1936 in Copenhagen (I do not even know whether this lesser known play by Brecht has been translated into English; my translation: the roundheads and the pointed heads). The author is Bert Brecht as has been presumed, but the composer (in this case) is Hanns Eisler. The German title is 'Die Ballade vom Wasserrad'.

Simon-Pierre,
I do not have the chords, but I have the score (Eisler's original score) for piano. If you'd like me to copy it for you, send me a private mail.

Wolfgang

Wolfgang