Victoria Wood on her new musical, That Day we Sang

So far, so Wood. In many ways, That Day we Sang is a showcase of the things that she is best known for: squeezing the humour out of the mundane and domestic; sharp social observation; an interest in characters with what Richard Ford calls “applause-less” lives; name-checks for Swarfega, Bournvita and American Tan tights. As in much of Wood’s later work, the comedy has a seam of nostalgia and regret.

The show epitomises its creator and her brand of Englishness. But That Day we Sang, which Wood has written, composed and directed, also has an unfamiliar element: alongside a cast including Olivier winner Jenna Russell and The Thick of It’s Vincent Franklin, it features a large children’s choir.

The show is based on a real event in 1929 when a group of Manchester schoolchildren made a hit recording of Nymphs and Shepherds; 40 years later, a TV documentary was made about their reunion. Wood’s story switches between these two time frames.

“For a long time I had the vague idea of doing a play about a child who went to that recording,” explains Wood, during a break in rehearsals (she has requested chips and, in case you were wondering, the correct answer to the vinegar question is “loads”). “Then I was in a meeting with Alex [Poots, director of the festival], who asked if I had any ideas for the festival, and said it’d be good if it had some connection with Manchester. So, I thought of this, and when I said it was about a children’s choir he said, ‘Well, we can start a children’s choir’. And suddenly, four schools had been marshalled.”

That can-do attitude of the festival must, one imagines, be a pleasant contrast to the restrictions and caution of TV. In an interview last year Wood bemoaned the lack of trust shown in her by the BBC. Today she is more circumspect on the subject. “Usually I can do my own thing and people don’t interfere. But with TV companies you usually get more input, you’re dealing with people who might not be creative, who obviously have a responsibility to their channel and their shareholders.”

Whereas, she says, with the MIF “we’ve got a huge cast, we’ve only got ten shows, we can’t make a profit. It’s nice to have that freedom. It’d be commercial suicide, but in a festival it is what it is.” The festival may not make a profit, but it is banking on That Day we Sang pulling in the crowds: ten performances adds up to some 18,000 tickets. Local schoolchildren will join Wood’s usual fan base: those of her generation who witnessed her emergence on the comedy scene in the 1980s; and those of us who first absorbed her work through our parents, with them tunelessly singing Let’s do It and doing impressions of Mrs Overall from Acorn Antiques.

Wood hasn’t cast herself in the show, even though her acting abilities are well-proven both in comic and serious roles. Won’t she be wishing that she was up there on opening night? “No, I’m not busting to drag Jenna off the stage. Acting is not the most exciting thing I do. I loathe wearing costumes, loathe wearing shoes with a high heel. I prefer characters who wear clothes like this,” she says, indicating her jeans, T-shirt and trainers. “I like being myself more than I like being other people.” The remark is indicative of an aspect of her character that has intrigued interviewers: being both overtly unassuming and intrinsically confident. Similarly, although she’s open and friendly in conversation, she also feels somehow out of reach.

Wood grew up in Bury, Lancashire, one of four siblings. Like Tubby in the show, her father worked in insurance; he was the witty one, says Wood, whereas her mother, “always claimed she had no sense of humour”.

Wood first realised that she was funny, she says, “when I was about 4. I wasn’t a huge show-off, but I used to sit at the piano and turn around, as if to the audience”. As a teenager she toyed with joining a rep company, “but I was short, fat and northern, I wouldn’t have got anywhere.” Instead she won New Faces, the talent show, in 1974, aged 21. “I was very ambitious and seized every chance I could. I thought, ‘I’ve always got that, at least. I’ve got a thing that I can do that I’m good at.’ You’re lucky if you have a talent, and it stays with you.”

While that drive and talent has driven a stellar career, Wood’s personal life has, as far as we know, been one of everywoman ordinariness. She has had well-publicised issues with food, and in 2002 separated from her husband, the magician Geoffrey Durham. She lives an unstarry life in North London, in an empty nest since her two grown-up children left for university. Due a holiday after 18 months of work, she plans “to do a big tidy up, potter, take things to the dump”. When asked whether her fame makes it difficult to observe people because they act differently around her, she says: “I think when people meet me and they find that I am very ordinary, they let their guard down.”

Does she feel comfortable in her role as a national treasure? “Oh no, I can’t bear that!” she says. Because it makes you feel old? “No, I don’t mind feeling old. I am old [for the record she’s 58, but looks much younger]. I just think there’s only room for one at a time. We’ve had Thora Hird and now it’s a toss-up between Judi Dench and Joanna Lumley. They can fight it out between them. I don’t want to be one.”

Why not? “Because a, it’s meaningless and stupid, and b, it boxes you in and people think of you in a certain way, in a National Trust, tea cosy sort of way. I don’t want to have a label.” But, she adds, “it doesn’t matter what people think about me, because they don’t know me.”

That Day we Sang is at Manchester Opera House, July 6-17. Box office: 0844 8472484; mif.co.uk