LONDON — Kate Middleton took one look at her lanky boyfriend, a young officer graduating from Britain’s military academy last month, and purred approval to two friends.

“I love the uniform,” she said. “It’s so, so sexy.”

Under most circumstances, such a comment would remain private.

But the dish in question was Prince William, heir to the British throne, eldest son of Princess Diana and Prince Charles.

And such is interest in the future king’s love life that television network ITN hired a lip reader to decipher his girlfriend’s every utterance.

Welcome to the world of the woman who might someday be Queen Catherine.

William hasn’t proposed yet, or even signaled such intent. But speculation was so intense that he might pop the question on Tuesday, Ms. Middleton’s 25th birthday, that by 6 a.m. more than 50 photographers and camera crews were waiting outside her apartment in London’s fashionable Chelsea neighborhood. Ms. Middleton does not have an official royal security detail, but police were called in to control the scrum, which blocked her way as she emerged to go to work.

Ms. Middleton has said virtually nothing in public — at least not audibly — since she and William, five months younger, met as students at St. Andrews University in Scotland.

But the English seem as sure as tomorrow’s rain that a new princess fairy tale is in the offing. Woolworths is so confident that the retailer is busily designing commemorative royal wedding tchotchkes, from mugs to mouse pads. Store officials said the company “missed out” in 2005 during the two-month engagement of William’s father and Camilla Parker Bowles — a multimillion-dollar slip that won’t be repeated.

Kate, as she is fast becoming known here (Kate Winslet and Kate Moss are still two-namers), is a middle-class descendant of a coal-mining family, with an art history degree and conservative hemlines. She is as English as thickly buttered toast, and roughly as controversial. Her courtship with William is chronicled by the press the way lions chronicle antelopes. They have been spotted smooching in the Alps, and they favor the London nightclub scene — often in the company of little brother Prince Harry, the Wild Child of Wales.

But through it all, Ms. Middleton has not stirred a wisp of controversy. She doesn’t smoke; she blushes. She shops with her mom (a former flight attendant who has an online business selling children’s party supplies).

“She’s a person you can relate to,” a sales assistant at Jigsaw, the clothing chain Ms. Middleton works for as an accessories buyer, Lily Laban, 20, said. “She’s not a million miles away from people her own age.” In perhaps her sauciest public moment, Ms. Middleton appeared during her college days in a charity fashion show modeling lingerie. But she looked more like an athletic teenager than a Victoria’s Secret model, and William was sitting in a $400 front-row seat adding a royal stamp of approval.

She has a fondness for stylish stockings, and the paparazzi here, who have an almost adolescent fascination with peeking up women’s skirts, have caught her a few times showing a little thigh as she steps out of her car. But even as the photo-bounty on her head soars (as much as $50,000 for an exclusive bikini shot, according to the Times of London), Ms. Middleton has confounded the paparazzi with clear eyes even at 3 a.m. and smart clothes that seem unwilling to wrinkle.

“She’s made no mistakes at all,” Penny Junor, who has written several books about the royal family, including a biography of Diana, said. “She seems self-assured. She’s got poise and grace. She looks good. She dresses well. She could be a perfect bride for William.”

Judith Watson, 41, an intensivecare nurse, says she has a good opinion of the “well-mannered” Ms. Middleton. “They seem to act like it’s the real thing,” she says of the couple. “I don’t think body language would lie. For example, in pictures, they look at each other a lot.”

Comparisons with Diana are inevitable, but there are many differences. Diana was a shy 19-year-old kindergarten teacher when she became engaged to Charles, the 32-year-old heir to the throne. William and Ms. Middleton are contemporaries who met at college and later shared a house with two other students. When William was considering dropping out, Ms. Middleton influenced him to switch to a less demanding course of study — geography — and remain in school, according to Robert Jobson, author of a biography called “William’s Princess.” In Mr. Jobson’s book, he quotes Ms. Middleton as saying William is “lucky to be going out with me,” the sort of confidence Diana seemed to come to much later in life.

While Diana endured her parents’ messy divorce, Ms. Middleton comes from a stable family background, where her parents run the online business together. “She seems to be much more grounded,” Ms. Junor says.

Royal watchers say palace handlers, using lessons learned from Diana, have given Ms. Middleton good advice and that, at least for the moment, she seems like a gift to the royal family.

“They need her,” Mr. Jobson says. “If the royal family is to be sustained, and if the monarch is to continue being relevant, they need to be relevant to the younger generation.”

Three of Queen Elizabeth II’s four children have divorced. The saga of Charles and Diana — and the other lovers crowded into their lives before, during and after their marriage — battered the royal family. Elizabeth remains one of the most respected and beloved figures in Britain, but many here wonder about the future, especially when it comes to Charles, who is generally regarded as a goodhearted if quirky man.

The queen, who is 80, is showing little sign of slowing down, and Charles is just 58. So it could be decades before William ever ascends to the throne. But William, by virtue of the sudden loss of his hugely popular mother when he was 15 and his largely dignified comportment since then, is a key to keeping the royal popularity ratings afloat.

“The royal family does need some young blood and some glamour,” Ms. Junor says. “They need stability. They’ve had an awful lot of upset in the last 20 years.”

Still, Ms. Junor said, a royal life could pose an extremely difficult challenge even for the most wellgrounded person. “I wouldn’t be in her shoes for all the tea in China,” she says. “It is a life sentence. … There must be something hugely seductive about being chosen by the man who will be king. But at her age, she has no real understanding of what it will involve. No one could.”

Robert Lacey, who wrote a biography of Queen Elizabeth II, notes that just a few blocks away in a London courtroom, a government inquiry is underway into the Paris car-crash death of Diana, who had been chased by aggressive paparazzi just before the 1997 accident.

“I thought the whole world would have learned,” Mr. Lacey says of the furious attention on Ms. Middleton. “It’s a rough, tough rite of passage, but she seems to be surviving it well.”