I thought they were going to sink into that cloud at the start! I fear this is the 1981 recording; various bits, such as the piano, sound identical, as does Nana's voice. (Nobody seems to mind though. Looks like it might have been a charity thing.) There's a lovely (though shorter) version at ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-w-PDmZXtN0s.html, with Peter Alexander - that's dated before 1976 so not that recording - I think it's genuinely live, as they duet.