This traipsing through Britain, this endless unpacking of the strange foreign tribe that is the royal family — it cannot end without an investigation into the subsistence traditions of the native peoples.

We are going to need to talk about McVitie’s.

The McVitie’s Digestive biscuit. The McVitie’s Rich Tea biscuit. The McVitie’s brand, which tastes like Britain itself, like the country’s past and future.

Lately, McVitie’s has been in the news because Prince William has requested a McVitie’s groom’s cake, based on a dessert he used to eat as a kid. The recipe circulated online: butter, chocolate, Rich Tea biscuits.

A palace aide has been ferrying back and forth from the London McVitie’s factory — the company also made Queen Elizabeth’s wedding cake — to make sure the design is right.

McVitie’s is bigger than the wedding. McVitie’s might be bigger — or more central to daily life — than the royal family.

Have a seat, love. Have a cookie. Have, at least, an omnipresent cookielike substance. Tea’s on.

But first, a gastronomical education. A biscuit primer from the most sumptuous British person we can think of.

Nigella Lawson? Please explain the McVitie’s biscuit.

“Ooh,” says the domestic goddess.

“Well,” Lawson says. “It’s plain. It’s the equivalent of the old-fashioned English nursery, where children were always made to eat a slice of bread before the slice of cake. In the cookie world, it’s the equivalent of the bread. It can go soft without losing its shape, and it doesn’t fall easily into your tea when you dunk it, and there’s something in the texture like wet sand that has been dried out, which sounds unpleasant but it’s not.”

What it is, literally: wheat flour, sugar, vegetable oil, raising agents. The digestive was invented in the 19th century as a digestion aid, Victorians being oddly preoccupied with their intestinal tracts. The Rich Tea is a more crackerlike alternative.

What it is, metaphorically: The McVitie’s biscuit is the unifying food of England. They are eaten after tea. Or they are eaten before tea. They are eaten as snacks. They pinch-hit for meals. Fifty-two McVitie’s biscuits are eaten every second. So beloved is the biscuit that Prime Minister Gordon Brown set off a firestorm dubbed “Biscuitgate” in 2009 when he refused to publicly declare allegiance to a particular flavor.

McVitie’s is what you eat because you are British because you eat McVitie’s.

Several years ago Lawson concocted a recipe for digestive biscuits and put it in one of her cookbooks.

“But it’s not quite the same,” she says. “This is one of those foods where the authentic version is made in the factory.”

To the factory, then. To the largest biscuit factory in Europe, where 27 million biscuits are produced every single day, where the air smells like hot sugar, in the northwest London neighborhood of Harlesden.

“Ninety-nine percent of British households purchased biscuits in the last year,” says Miranda Lacaze, who works for the McVitie’s parent corporation, United Biscuits. That’s according to a survey done by Kantar Worldpanel, a European market research firm. “Only 95 percent said they bought toilet paper,” Lacaze continues. She pauses. “I don’t really want to know what the other 5 percent are.”

Lacaze, Harlesden factory manager Andy Brammer and a McVitie’s corporate type named Bob Brightwell are all sitting in a conference room, drinking tea and eating biscuits. It’s a calm, soothing atmosphere.

“They’ve been around since 1892,” Brightwell proudly says of his humble product. The McVitie’s recipe was developed then by Alexander Grant, whose portrait adorns the wall. “You have a tea, you have a coffee, you have a biscuit.”

“In the 1920s” — Brightwell continues the oral history — “someone said, ‘Let’s put chocolate on them,’ ” so they did. “We have a caramel one,” and a diet version, and one that’s ginger-flavored.

The other day, Brightwell mentioned to his nutritionist that he frequently had a couple of digestives for breakfast. “She said, ‘That’s not right. You need dairy! You need whole grains!’ And what does that describe? A digestive biscuit!”

A few floors down, in the factory, some 550 workers work 11 different lines to keep up with production — rows and rows of dough being punched into rounds, stamped with the McVitie’s signature image of wheat, then baked in a conveyor belt oven. The chocolate ones must go through “enrobing.”

Here in the factory, one can see the subtle difference between the McVitie’s Digestive, which crumbles, and the Rich Tea, which snaps. (The snappiness is a key trait of the Rich Tea, the McVitie’s crew explains.)

“Don’t worry about the broken ones in the bins,” Brightwell says, assuring visitors that nothing in the factory goes to waste. “They are used for cheesecake crusts and such.”

Instead of graham crackers?

Brightwell looks pleasantly bemused by this question.

“What,” he asks, “is a graham cracker?”

What is a graham cracker, indeed.

The English are very similar to us, except for their food, which means they are not similar at all. Any fool who has ever attempted to spy on a party host by snooping in the medicine cabinet has totally missed the boat. The real personality-defining information? It’s in the fridge.

This week, for thousands of tourists, Britain opened up its collective refrigerator to display its native, everyday cuisine. Mushy peas, jacket potatoes, pork pies. Foods that are reliable and don’t try too hard to impress.

Extrapolating meaning from a tea biscuit is a bit like extrapolating meaning from tea leaves, which is to say, you can probably find meaning if you’re looking for it. But we can all agree on this: A tea biscuit means tea. Tea means sitting down with a proper cup. A cup might mean a table and perhaps a napkin. Nothing about a messy biscuit says “on the go.” Nothing about it is fast or inventive. There is no expectation that it should be particularly delicious; there is no expectation that life should be particularly delicious.

Although the rest of the cooking world is obsessed with artisanal — every baked good a unique, hand-formed art project — McVitie’s is a champion of sameness. The biscuits are spot-checked for uniform consistency and thickness.

The digestive biscuit is much like the monarchy. You have it because it is there, because it is what you do, because were it not for the royal family and the digestive biscuit, the United Kingdom would be like America.

In 1974, the famed food anthropologist Mary Douglas published a seminal treatise on the British way of eating. She described the various types of meals Britons might eat and under what circumstances. Biscuits received their own category, as “a summary form of all courses.”

Douglas’s entire article — this whole exploration of what it meant to be British and eat food — was titled, “Taking the Biscuit.”

“The cake will be in buffet slices,” Brightwell says of Prince William’s royal biscuit masterpiece. About 500 slices, made from about 1,700 biscuits and about 17 kilos of chocolate. They have to wait until the last minute to make it. “If you make it too soon, it gets less snappy. The whole point is that it’s snappy.” They will be making a backup cake, just in case something goes wrong with the first. McVitie’s is taking its cake-making responsibilities very seriously.

But the wedding is only one day.

Then it will end.

And an entire country of exhausted parade watchers and wedding lovers will return to their homes, to recap the day and have a little nosh. You know what they will eat.