Victoria Wood says in the programme notes that the idea for the musical came from a documentary about the recording that she saw in the 1970s, featuring interviews with people who had been in the choir in 1929 and were by then middle-aged. Her musical is set in 1929 and 1969, based around the two main characters meeting at a choir reunion after 40 years, hearing the record again and remembering how their 10-year-old selves had felt on that day. They start to ask themselves whether they can together rescue their lives from the mundane routine they have sunk into and live the more joyful life that once seemed possible. And of course, it is very funny and entertaining. It is not the 1960s of Mary Quant, Twiggy, mini-skirts and Vidal Sassooon haircuts, but of Berni Inns, The Golden Egg and Wimpy Bars. (The audience were mainly of an age to remember all those things and were very appreciative.) There is a wonderful song-and-dance routine around dinner at a Berni Inn (melon and maraschino cherry or prawn cocktail, gammon and pineapple, and of course Black Forest gateau).
The 1929 thread in the musical has a choir of local primary school children, playing the original choir, and an 11 year-old actor playing the younger version of one of the main characters. He does a fantastic job - it is a big part involving singing, dancing and speaking, and this was his professional debut. There is a YouTube video showing brief extracts from the opening night, so you can see how well the children did.
And you can also hear the original recording on YouTube. The choir mistress in 1929 trained the children to sing for the recording in "received pronunciation" rather than with their usual Mancunian accents - fortunately today's choir sing with their natural vowels.