I Don't Know How She Does It

She first met Allison Pearson at a Nativity play. Their eldest daughters, Polly, seven, and Evie, six, both went to the same school in Islington. They vowed to see more of each other, never had the time and so "e-mails became our coffee mornings instead. I'd e-mail Allison about what a dreadful 'Kate' day I'd had - being late for work, no cabs, nine reports to write by lunchtime. Then we started doing Pilates together. We'd meet every week and do tummy-button-to-spine stomach exercises on Allison's floor."

When Allison was wondering where to set her Daily Telegraph column about an overwrought working mother, it was Miranda who suggested the City. "It is the most extreme example of long hours and family-unfriendly working policies," she says. The existence of one's children was kept under wraps. "I never discussed mine, unless with other mothers.

"There aren't many women I know who would even have photographs of their children on their desks, whereas the men always would." Sometimes the telltale clues, like baby sick on the jacket, sneaked out. When that happens to Kate, there are gleeful whispers of "she's not coping", prompting the "kit inspection" she puts herself through every morning. Kate's worst kit catastrophe is the red sex-siren bra screeching through her white shirt during a presentation (she'd dressed in the dark). Miranda's was the bad-shoe moment: "I had two pairs that were identical, one black, one navy blue," she says. "When I got to work I realised I was wearing one of each. I kept my feet under the desk all day, and when I did get up I walked around in stockinged feet."

Not coping justifies being sidelined to the Mummy-track, and if you think you can be the high-flyer you were before babies, forget it. Or, as Kate puts it, "you're either a babe, a mumsy or a grandma".

Miranda winged it in the babe category, even after Polly was born. That, she explains, is because "I was unusual, by being prepared to travel despite having children". By the time Theodora was born, Miranda was travelling to Milan at least once a fortnight.

"The car would collect me at 5am. I'd usually get back at 10 or 11pm. Because I was working bloody hard, Nick did most of the night-time stuff.

I could not have had three children and worked in the City without him and our nanny, Lianne." Nick, she says, glowing, is a "paragon" of a hands-on, tuned-in father and very supportive husband.

Then, last September, Miranda went part-time. "They weren't awfully good at giving me any support," she says. "I really needed eyes and ears in London for the two days that I wasn't there, but that wasn't forthcoming. Without that support I couldn't do my job properly and there was no point carrying on. I'd never done my job badly and I wasn't prepared to do so now. I felt I had very little option but to leave.

"There had been a change in management structure. They clearly didn't approve of me working part-time. I am not sure how keen they are now on women working either. One of my bosses told me he didn't approve of working mothers, that they should stay at home, and that he hadn't let his own wife work while his children were young."

She recalls recommending a female colleague for promotion to a more senior male colleague. "But what about her commitment?" he said. "What about her commitment?"

Miranda replied. "She has two children," he replied. "So have you," replied Miranda. "In the end, a chap got the promotion over two women, both mothers, who had six years more experience than he did."

Kate fears that if she were to become a full-time mother she would not only be frying her children for breakfast, she would become one of the "Domestic Disappeared".

Not so Miranda. While Kate simulates home-made mince pies for her daughter's Christmas party by crushing Sainsbury's best with a rolling pin, Miranda makes her own mincemeat. "I enjoy cooking, it's relaxing," she says. Fair enough. But I'd call baking a birthday cake when you should be in the bath with a whisky a classic Kate moment: "I got back from Milan at 11pm and made Polly's birthday cake, then iced it the following morning. I know she would have been just as happy with a Barbie cake, probably happier, but I just wanted to make it." That said, once she'd resigned, Miranda looked ahead to her new life with a degree of trepidation. Not so her children.

"When I told them I wasn't going to work any more, Polly's smile spread from here to here," she says, drawing a line right across her face, "and Millie went 'yes!' and punched the air.

"I warned them it would be a period of adjustment, that I might get very angry and shout at them a lot and run out of patience and they might hate it. Polly just said: 'I don't mind if you shout, mummy.'"

"The biggest difficulty," she says, echoing fears of Kate's, "is not having a salary, having to say, I need money to pay the cleaner, or don't send the bill to me, send it to Mr Richards."

Miranda grew up in Newcastle upon Tyne; her father is a retired classical musician, her mother a book editor. Although her work is part of her identity, it has neither defined nor subsumed her in the way it does Kate. Which is why, when she ran into a fellow student from St Andrew's University, and he asked what she did, she replied, "I look after the children."

"It was the first time I'd said it.

Normally, my reply would be, 'I used to be a fund manager in the City'. Saying I was a mum made me feel great, I felt I was doing something of value and that it was a choice I made off my own bat."

After tea, Miranda and Theodora take me to see if the chickens have laid any eggs. Polly flies past on her bike, Millie, five, climbs on the trampoline and I feel as if I'm going to cry, it all seems so perfect.

Then Miranda says: "Local friends who are full-time mums used to say to me, 'I don't know how you do it.' But I look at them and think, they are so organised, I am still adjusting, I am not there yet." Then she adds: "I can't see myself doing this forever."

Neither can I. Driving to the station, I notice a dictaphone by the gear stick. Miranda uses it to list the day's tasks. "Whoops! that makes me look a bit Kate!" she laughs. She's already a consultant on the film of the book, and other plans include becoming a pension-fund trustee, a magistrate and a company director. And she's expecting her fourth child in November.

I don't know how she does it.