Now a Guardian article - Michael Hann
“Red Lion House used to be a pub – which was a very good sign, especially to folk singers – and we got on like a house on fire,” Kerr says. “John and I were very leftwing: Oliver’s father had written the definitive history of the trade union movement, and his uncle was [1930s Labour leader] George Lansbury. We had all kinds of links.”

Faulkner says: “He explained what these programmes were about, and they were sort of experimental, in the sense that he liked the idea of using music that was traditional-based, because the stories he had written were very folky. He wanted something more bedrock, and we could provide the kinds of instruments I don’t think he’d considered – autoharp, mandolin, concertina.”

Both remember making the Bagpuss music to be a delight. Postgate would tell them the stories he was telling in the episodes, sometimes supplying them with lyrics to set to music, and they would compose around his suggestions. “He would give us a lyric, like The Bony King of Nowhere,” Faulkner says, “and say: ‘Can you write a melody for that?’ We would go away and throw it around, then record a tune to cassette. ...

... The pair were inspired by many different strands of traditional music of the British Isles: the Irish traditional song Brian O’Lynn makes an appearance; for The Weaving Song, they set Postgate’s words to an old Scottish tune called The Calton Weaver. One of the most recognisable pieces – the mouse round, We Will Fix It – dated back centuries. “I think we had just recorded Sumer Is Icumen In with the Critics Group,” Kerr says, “and, when Oliver said he wanted a little round, that must have been in my head.”

 https://www.theguardian.com/music/2018/nov/20/story-bagpusss-magical-folk-soundtrack-sandra-kerr-john-faulkner-oliver-postgate?fbclid=IwAR11UuXNLRb-p_v398RQp3z0VPMBw10nEBM64cr7IdRyLzaUH3LDG5x627A