How are things with your mum? A gentle question, but it stops Davina McCall dead. The smiley, quick-witted woman who has been chatting away at the Groucho Club in Soho for half an hour or so goes very quiet.
"Erm," she says after a while. "With my real mum?"
Yes, sorry. The one who gave you up at the age of three, I want to say. The one who moved to another country rather than raise you, but who told a reporter last summer – in an interview drenched in bitterness and self-pity – that it is she who feels abandoned.
"I think...." The words come out slowly. Davina, calm in the emotional chaos of all those evictions on the television show she hosts, Big Brother, seems hardly able to speak. This star who came in wearing a long, fluffy coat of bright green fake fur has shrunk into her chair. The gift she has for keeping up eye contact, making you feel like you're her new best friend, has vanished; she is staring at the floor, and I realise she is nearly crying. "It is ... sad."
Silence again. This is too much, actually. Worrying, I offer to turn the tape recorder off. Maybe we should go back to talking about Sport Relief, the telethon she will present on Friday night; or its mass run on Sunday which may be the biggest collective sporting effort ever in this country. Or the visits to Africa that have made her so committed to the cause. "No, no," she says. "I don't mind. I have no secrets, at the end of the day."
That's a dangerous policy, surely, for one of our biggest TV stars, but it may also be true. She has spoken before about the horrendous mess she got herself into as a young woman. The former pupil of Godolphin and Latymer School, brought up by a loving granny and then her father and stepmother (the "Mum!" she talks to in those ads she does for hair dye), became addicted to hard drugs, including cocaine and heroin. That was before Narcotics Anonymous and the help of Eric Clapton, a friend of the family, who encouraged her to audition as a presenter for MTV.
Davina is 40 now and first-name famous, mostly for acting like a big sister to the attention-hungry, the troubled and the (frankly) freakish on Big Brother. Despite her fame, she shows the recovering addict's willingness to face a question with honesty. "All my life I have thought I must go and talk to a therapist about my mum," she says, "but I've never really felt in a safe enough place with the rest of my life until now. I've done, like, getting clean [from drugs] and all the self-improvement that takes, but this is different. In any life, the most important relationship is with your mother."
Hers was called Florence. Born in France, she was a free spirit (and an alcoholic) who returned to Paris, allowing her daughter holidays so wild she never felt able to tell anyone back home. These days Florence communicates by fax, to the office of Davina's husband Matthew Robertson, who runs an adventure travel company. "My mother sent me a fax last year, saying, 'This guy is on my back, please can you get him to go away? I can't remember very much, I'm not very well at the moment'."
The guy in question was a reporter for a British tabloid. "I got someone to call him and say 'Leave my mother alone, she's really sick'. And he went, 'I'm very sorry to tell you this but her first question was, 'How much will I get?'" That was "the final straw" that drove Davina into therapy, she says. "I have to stop rationalising her actions towards me and just say, 'That's not very nice'."
She is shocked that tears have come this morning. "I have shut down, feelings-wise, about this," she says, then changes her mind. "I feel a lot. Sometimes in a good way ... and sometimes it's really fucking painful."
The tears actually started in the car, on the way up to the West End from her home in Surrey, when she was watching a DVD of the series Brothers and Sisters. "The daughter in it was my sort of age, but she was frightened of the wind. The mother said, 'Come on, you can stay the night in my bed'. It just made me really sad. It's like, right there." She makes a fist and thumps the middle of her chest, then smiles weakly and says: "I've had a bit of a moment, haven't I?"
Calming herself, she says: "There's a whole history that goes very deep. It was really hard. I'm sure it's hard for her. It's ongoing, and unresolved." They're not talking then, I take it? "No. Because of that article. I can't get hold of her anyway. She sent a fax recently asking for something – money, I send her some every month anyway to help her live – but there was no return number at the top of the fax. It's anonymous. I have no telephone number, no email. All I have is a post box number. I'm handcuffed. It's very frustrating."
She grabs the napkin on which her café latte rests, ignores its sogginess and blows her nose. "I'm fine, honestly. I'm not a person on the verge of a nervous breakdown. You've just got my achilles heel."
Her own children were deliberately conceived at a time of year that allowed her to go on doing Big Brother, which is back in May. Holly, Tilly and Chester, aged six, four and one, were all born in September, safely distant from the show. "My press officer has already started taking calls about whether I'm pregnant or not, which is hilarious." She's not, then? "No. We've drawn a line under that, in the way that adults can!"
BB has got nastier and more bizarre over the years, but she still manages to talk to contestants as if they are on empowering journeys of self-discovery. What about the ferocious criticism it has received? "Who gives a shit?" she says, perking up. "If nobody was watching it and I got a lot of flak then hey, I'd be quite depressed. But it's going really well. I couldn't give a rat's arse."
She has had big flops, including a chat show the BBC hyped madly then pulled quickly, but as her Big Brother boss Peter Bazalgette says: "Because people think she is their friend, they don't hold a poor show against her."
When she hosts Sport Relief on Friday night, celebrities will perform increasingly unlikely physical feats for charity. Davina too will run the Sport Relief Mile on Sunday with up to half a million people across the country (some actually running six miles, like her). She's in the gym all the time, presumably? "If that was true I would look like Madonna. No! Look."
She flexes a bicep, then jiggles the flesh underneath. "A little bit of a bingo wing." Then she lifts her jumper, to grab her tummy through a blue and white stripy t-shirt. "There. A jelly belly." It's true. She has a normal body, like a fan might have... if she could hire fitness instructors to visit her house three times a week.
The last Sport Relief event, two years ago, raised £18m – but isn't there something absurd in hugely wealthy stars asking the public to donate the £2 they say it takes to feed a "street child" in India for a week? "So let's hire a new, penniless presenter nobody has heard of. Do you think people are going to tune in? No!" she says, in that mock-bolshie, sharing-the-joke manner she uses on telly. Surely the stars could do a lot of good by swishing their own wallets? "And we do. How do you know we don't?"
Fair point. All Sport Relief's costs are paid by sponsors, so every pound goes directly to projects such as the one she visited in Samburu in rural northern Kenya. There she met a woman who had lost three of her children and her husband to a drought. "Obviously we had a very serious and sad chat about that. It was agony. I was saying, 'Look, I know this is hard, but I'm just trying to show how badly drought affects families."
Then things changed, in a very Davina way. "This woman's girlfriends came round, and we all started talking about childbirth. I said my husband was with me, and they thought that was hilarious. Then I was proudly telling them I had my babies at home, thinking they might find that impressive, and they were like, 'Yeah, but everybody does that, right? Big deal! What's a hospital?'"
Empathy is what she does. "I love moments like those, when you're on the same wavelength as somebody even though they live in a totally different country, with a totally different culture and language... you're just two mums having a chat about childbirth. It's great."
She sighs. Davina could talk about motherhood all day long, but the words to express her feelings about being a daughter are only just beginning to come. "I need to iron out my relationship with my mother, and what she means to me," she says, "and why it hurts so much." She leans forward, touches my knee like a friend, and smiles as if to reassure. "I'll be okay. I will. I like being a work in progress. I couldn't face it, you know, if I didn't feel so happy and safe in the rest of my life."
To donate, or sign up to run, go to www.sportrelief.com