As is so often the case these days, it is a Spice Girl who comes up with the appropriate sentiment. Emma Bunton ("Baby Spice"), turns to the camera during "Stars and Mas", an Omnibus film about celebrities' mothers, and declares that: "A mother is for life, not just for Christmas."

She's absolutely right, of course. The film merely underlines the reality that, try as we might to break free, we're manacled to our mothers for the duration. Phillipa Walker, who produced the documentary, takes up the theme. "The original notion for the film was that you are your mother's child. Either through rejecting or embracing her, you can't but be your mother's child. For instance, my mother is a role model in the way I bring up my children. But also I'm very neat and tidy, and that's a direct reaction to the way she was."

Walker, who has made a film about American novelist John Cheever's family and is planning one on the Guinness dynasty, contends that all human life is found within the family unit. "If you get to the nitty-gritty of it," she argues, "there's nothing else like it."

Some of the family relationships highlighted in "Stars and Mas" - receiving a timely Mothering Sunday screening tomorrow - are not a pretty sight. Soon after the actress Claire Bloom started going out with the writer Philip Roth, he wrote her a letter telling her she would have to choose between him and her 18-year-old daughter, Anna Steiger. As mother and daughter sit uneasily side-by-side in this film, Steiger shakes her head and raises her eyebrows during Bloom's rationalisation of her decision to go with Roth and abandon her. "I just feel there's a lot of whitewash going on here," Steiger sighs, "and there's an element of bullshit, frankly, in what I'm hearing, and I don't like it."

The obvious tensions between them make for gripping television. Steiger claims that even at the age of five, "I thought that she [her mother] was a weaker character than me... I don't think my mother was ever told, `No, you can't'."

"What is interesting," Walker reckons, "is that you see the influence of Claire's relationship with her own mother, how those patterns are embedded in her, and how, almost against her will, she seeks to revisit them. [And] she brings a lot of baggage from that to her relationship with Anna."

Later in the film, Bloom breaks down in front of the cameras as she recalls her period with Roth. Steiger says knowingly that, for programme-makers, "the bad times are so much more interesting." But Walker rejects any suggestion that this is voyeuristic. "That's another debate," she reasons. "My view as a documentary film-maker is that when people offer experiences it is valuable to the people watching. Lots of people will have gone through the same struggles and will empathise. I try to be as honest and open with people as I can. I explain as much as I can in advance. I don't want to be in a position where people are feeling, `Did they go too far?'"

What this sensitively handled film does best is emphasise the closeness of the bond between mother and child. Witness this touching assertion by Violet Blake, the mother of boxer Lennox Lewis: "I let them pull him out if I see that he's going to get hurt. I don't care about the belt, I don't care about the money - I care about my son."

But it is a Spice Girl who has the last word. Emma Bunton speaks for many when she says that, despite her sudden fame, she and her mother are still like flatmates: "The most rebellious stage I was at was coming in 10 minutes late ... But we haven't changed, have we? We're the same. We still watch EastEnders and eat chocolate Rolos and McDonalds."

Omnibus's `Stars and Mas' is on tomorrow at 10.15pm on BBC1