Across the street, TV camera crews and photographers have staked out spots on the sidewalk facing the private Lindo wing of St. Mary's hospital, hoping they've snagged the best vantage points to get the first pictures of Prince William and Kate holding their first child.
Even the doctor expected to be in charge of the royal baby's delivery has reportedly told people he has stopped drinking so he can be ready at a moment's notice, the Daily Telegraph said Wednesday.
Buckingham Palace, which carefully and strategically does what it can to mould the public image of the House of Windsor, has a detailed plan for how the blessed event will be announced to the world.
But babies can be notoriously unpredictable when it comes to their arrival, and with the way social media now spreads fact and fiction instantly, there could still be a few surprises as the third in line to the throne makes his or her appearance.
Bonnie Brownlee, CBC's royal commentator, says the palace will let everyone know once Kate is comfortably ensconced in her hospital bed, awaiting her delivery.
"Can she get into the hospital without the rest of the world knowing — that's a crapshoot," says Brownlee, noting that reporters are already outside St. Mary's, and are also staking out another hospital closer to Kate's parents' home outside London, which is also ready for a royal birth.
"They're going to try to get her into hospital without reporters seeing her," says Brownlee. "There are ways of doing it, but I think everyone may have figured that out."
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Kate did manage to get into hospital unnoticed in December when she had acute morning sickness, but her pregnancy hadn't been announced, and no one was on the lookout for a royal hospital run at that time.
It is different now, however, and those who keep a close eye on royal comings and goings in London know all the clues, right down to the licence plates on the royal vehicles.
"They'll know the car. Even if she switched to another one, everybody knows their cars," says Brownlee.
While all hints — official and otherwise — have suggested a due date of around July 13, media speculation ramped up this week that an earlier arrival might be in the cards.
"Duchess of Cambridge: are we expecting an early royal birth?" the Daily Telegraph asked Wednesday, noting that the TV crews were on hand, rumours were swirling on social media and bookies have slashed the odds "for a delivery as soon as this week."
Add to all that the widely reported suggestion that Prince William's own mother, Diana, played her own little bit of media manipulation with his 1982 due date, saying it was later than his birth turned out to be, and it's anyone's guess what Kate's due date really is.
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Still, no matter how the birth unfolds, there's a carefully scripted plan in place as the palace tries to control how the world will learn the first details about the third in line to the throne.
Brownlee says it's a mix of the traditional and the modern, all based on trying to give Kate and William as much leeway as possible in having a child on their own terms.
'As vulnerable as any other couple'
That, of course, isn't likely to happen — this baby will be born a prince or princess.
"But once they get into the hospital, they will have a baby like any other couple and at that moment they will be as vulnerable as any other couple having a child," says Brownlee.
"All you can hope for and wish for is that it is a good and easy birth, and that the child is healthy."
Palace officials have said Prince William, who has been working as a Royal Air Force search and rescue pilot in Wales, has every intention of being at the birth. But, depending on timing, he may have to be flown or drive back to London and not be there when Kate goes into hospital. Kate's mother, Carole Middleton, and sister, Pippa, are also likely to be at the hospital.
The public announcement of the birth won't come until the Queen and family members, as well as British Prime Minister David Cameron, and governors general of the 16 Commonwealth realms — including Canada's David Johnston — have been informed.
Once that's done, the two senior doctors overseeing the birth will sign the official announcement on Buckingham Palace stationery. Palace officials say it will be carried out of the hospital through the main door of the Lindo wing, and driven to Buckingham Palace, where it will be displayed on an easel in the forecourt, as per tradition.
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All that is part of what a palace official has called the "theatre" of the moment, and to ensure the announcement is made with a nod to historical precedence.
The easel is the same one that held William’s birth announcement on June 21, 1982.
Waiting for the name
"In old and traditional days, you would walk by and that's how you find out or people would gather and wait for the information to be placed on the easel," says Brownlee.
The announcement will include the sex and weight of the baby and the time of birth. There’s no guarantee, however, that the name will be announced at that time — it took six days before William's name was known, although the name of his younger brother, Prince Harry, was made public within hours of his arrival on Sept. 15, 1984.
If the birth occurs in the middle of the night, tradition dictates that the Queen not be woken up and officially informed, which means no official announcement on the easel would come before 8 a.m. London time, Brownlee says.
That's not to say people won't start to figure out something's up, or that William wouldn’t have made a quick call to his grandmother, the Queen. Reporters outside the hospital might catch wind of a few details, or Kate and William might decide to call a few friends with their good news.
"It may be leaked 100 different ways," says Brownlee, "but they [in the palace] will stick to their tradition."
The birth, which the palace will also announce later the same day on social media, will set off a frenzy of public celebration in London.
"The buntings will be up, the champagne will be flowing," says Brownlee.
"There'll be street parties. They're already starting to do some of that, so it's only going to get more and more exciting."