Sally Williams sizes up the service at John Lewis's lingerie department

Mary, 51, lovingly dusts a display of Berlei Shock Absorbers, Warner Doreens and Silhouette Paysannes. Mary works in Boxed Bras, in the lingerie department of John Lewis, Oxford Street. She has been in bras for 30 years."I definitely remember people by their bra rather than by their face," she says. One of 10 trained bra-fitters in the department Mary's job is to size up breasts: soft and firm, big and small, reduced and enlarged, even absent following mastectomies. She is unmarried, has a cat called Major and spends her weekends spying on other lingerie departments. Jennifer, 34, in Co-ordinates (matching bra and pants), is hanging newly delivered silk/satin turquoise cami-knickers and bras on the display rail. Ann, 44, weaves her way around the mannequins (today's outfit: fuscia Wonderbras), putting stock from the 18-boothed changing room back in the correct place. Christine, departmental manager, bustles through Woven Thermals, organising coffee, lunch and tea breaks of her 40 staff members.


Opening time. The first customers arrive. "Find a fitting room and press the switch next to the mirror," says Ann to a young girl with a selection of frothy lace basques. A buzzer sounds and a light flashes next to number eight on a panel outside the fitting rooms. "Oh God," says Christine, "the bells have started."


Mary's first customer is a heavily pregnant woman. "I need more support," she says. Mary leads her into fitting room five carrying a selection of shock absorbers including a sports bra, but, says Mary, "perfect for heavy, stretched breasts".


In cubicle ten, a woman is insisting she is a 36B. "She's definitely a 40DD", says Mary. Seventy per cent of women wear the wrong size. Mary reveals a strategy: "I won't tell her outright she's a 40. She'll blow a fuse. I shall take in this 38D; of course, she won't be able to breathe. Then I'll whip on the 40DD and she'll be so relieved, she'll go for it." Protestations are soothed by blaming the bra: "The Passionate always comes up big, Madam."


The 40DD walks away pounds 80 lighter after buying three bras. Assistants don't get a commission, but do, being "partners" in the John Lewis co-operative, share in profits.


Jennifer is addressing a re-shaping problem: "I have a customer with a fuller figure who wants to look pointed." She selects a Fantasie 38FF, "not too constructed, and perfect for lifting". As well as being 96 different sizes, fitters must know their push-up from push-in bras as well as the idiosyncrasies of each make.


Mary is on her lunch break - 45 minutes with a cheese sandwich in the Partners' Dining Room. Lynda, 31, is showing an Indian gentleman a sports bra. "They look so good under T-shirts," she enthuses. He takes one, along with eight others "for my wife". "Men do get embarrassed," says Lynda, "but I walk them around the black and red range and they mellow out." Apparently, men will often trot out a measurement - their girlfriend's height.


It's the lunchtime rush and fitting room 11 is impatient. Christine is discussing a problem with Lucy from Visual Display. "I'm not happy with how Woven Thermals goes into Glamour - can I have a mannequin to divide the areas?"


A customer phones to say her Shock Absorbers has shrunk. "She bought two and one has shrunk in the wash," explains Christine. The customer is told to bring the bra in.


"Ouch - that bone shouldn't be digging in there," says Mary, from fitting room three. "Do you swim or sing?" "Well, I do the odd length," comes the somewhat bewildered reply. "That's it, then" says Mary, triumphantly. "You're diaphragm has lifted up."


Mary is in fitting room three negotiating a breast reduction. The customer was a 36F and is fixed on being a 34B. "She is really 36D", says Mary, but she won't have it." Mary persuades the customer to wait until the plaster is off and swelling has gone down.


Ann is dispatched by a young woman with big hair and lip gloss to find a thong. "It must be plain, not satin and it must match this bra," she orders. Mary eats a scone. A young man sits at the feet of a mannequin reading a book,. Girlfriend is buying a sports bra. "She won't be long," he says.


A lady phones to check if Mary will be working on Thursday. Mary fitted her last year and she wants to be fitted by her again. The "shrunk" Shock Absorber turns out to have been the wrong size. "It was a D, when it should have been a DD," says Christine. The bra is exchanged. The boy by the mannequin is reunited with his girlfriend, but only temporarily. "What do you mean, you've only been measured?"


"Where are the Sloggies?" asks a woman dropping by after work. The waiting boy's girlfriend finally emerges with a cross-over sports bra. "That's it. We're going home," he snaps as she tries to show him the bra.


Closing time. Mary tidies her boxes. Fitting room seven can't decide; Ann's smile starts to flag. Christine gathers the department and reads the sales figures. Mary met her target. She goes home satisfied to Norwood, Major and her vegetarian meal for one.