The British arrived.

Brilliant!

For the British, we roll out our most glorious specimen. For the British, we bring out The Clooney.

The purpose of a state dinner is always to cement relationships, celebrate ties, create photo-ops. But diplomatic canoodling reaches a treacly pinnacle when the guests in question are our special friends from across the Pond — as they were at Wednesday’s White House party.

The U.K. was in top form, whispering sweet nothings with clipped consonants. “Barack, it is an honor to call you an ally, a partner and a friend,” Prime Minister David Cameron said in his toast to the president. “It is a pleasure to work with someone with the moral strength, with clear reason and with fundamental decency in this task of renewing our great national alliance for today and for the generations to follow.”

America was in equally top form, showing off for the country we declared independence from 230-plus years ago and have held in soft focus almost ever since. “In war and in peace, in times of plenty and in times of hardship, we stand tall, and proud, and strong together,” President Obama said as he raised his glass to Cameron.

Technically — technically — this is an official visit, not a state visit (no queen, the head of state), but the White House decided to call the meal portion a “state dinner,” and, really, who are we to quibble? Besides, this means that the White House gets to host Cameron and his chic wife, Samantha, who wore a blue patterned Alessandra Rich gown. Michelle Obama wore blue, too — a deep teal Marchesa designed by Georgina Chapman, a guest at the dinner.

The 362 guests — the largest state dinner of this administration — demonstrated the reciprocal relationship the United States and the U.K. have with each other’s pretty celebrities.

British actor Damian Lewis, last seen as an American POW trying to assassinate the vice president on Showtime’s “Homeland,” was there — Obama’s a huge fan of the show. “When does he watch TV?” the actor wondered, ambling past the press line on his way into the dinner. “That’s what I’m going to ask him.” Lewis brought his wife, Helen McCrory, better known to Americans as Harry Potter’s Narcissa Malfoy.

In terms of British cultural imports, the score at the dinner was Downton Abbey 2, Harry Potter 1. Both Hugh Bonneville and Elizabeth McGovern (Lord and Lady Grantham!) were there, the former commenting that Britain’s relationship with the United States “was symbolized in the show with me being married to an American.” The latter wore a daring mesh gown and looked hotter, older, sharper than her dizzy, slurring onscreen character.

More star power: PBS’s Gwen Ifill brought “The Wire” actor Wendell Pierce (Bunk!). BET head Debra Lee hitched up her dress to reveal teetering hot pink shoes, designed by Brian Atwood. Anna Wintour, teeny as a human Q-tip, wore black and white Chanel. Richard Branson’s lion mane was there, as were Warren Buffett’s delightful grandpa glasses, and there was a strong showing of gay power couples (blogger Andrew Sullivan and his husband, Aaron Tone).

The requisite government types made the list, as they must: the John Kerrys and Eric Holders and Antonin Scalias. Hunter Biden came. We demand that the gorgeous Biden children arrange a runway walk-off with the gorgeous Romney children immediately.

When George Clooney finally arrived — avec entourage — he breezed past reporters but gestured to the people with him, who included human rights activist John Prendergast. “Get some pictures of these very smart people,” Clooney encouraged the press, who did not like this idea.

“Don’t go,” one female reporter whispered as he disappeared.

But he must go! He must go hear performances by John Legend and British folk-rockers Mumford & Sons, whose music evokes frolicking double-date road trips rather than fusty governmental sit-downs.

He must be ferried by trolley to the tent set up on the South Lawn, decorated with pillar candles and purple carpet, and flower boxes evoking American and English gardens.

The British government and British crown have begun 2012 by embarking on an unofficial goodwill tour, promoting London’s Summer Olympics, promoting Queen Elizabeth II’s Diamond Jubilee. Prince Harry has been gallivanting around the Caribbean, dancing in Jamaica, gamboling down a track with Usain Bolt.

Cameron’s visit also marks another anniversary — 200 years since British troops invaded Washington and burned the White House. (All’s forgiven, mates.)

After all, they’ve given us so much: Kate Winslet, Adele, English, Cadbury Creme Eggs.

We, in turn, gave them outdoor grilling. The president, earlier on Wednesday, presented the prime minister with a wood- and charcoal-burning Braten 1000 Series Grill, commemorating a spring visit to Downing Street last year, in which the two first couples grilled together and served food to members of the armed services.

And what weather we’ve been having — perfect for a cookout. Alas, Cameron flipped no burgers. (But Obama made jokes about it.)

The menu, as usual, was a commercial for the first lady’s backyard garden. Chefs harvested veggies and greens for the four-course American meal with small nods to British tastes: Alaskan halibut with baby kale, green salad, bison Wellington and steamed lemon pudding. After criticisms that the Obamas served a pricey wine at the state dinner for Chinese President Hu Jintao last year, the White House has stopped releasing the names of specific labels. For this dinner, the White House merely told reporters that “an American wine will be paired with each course.”

It was a lovely evening. Good friends hosted good friends. Accents mingled in their common language. The president placed his favorite “Homeland” star at the head table. The first lady, representing all women, both American and from abroad, seated herself next to The Clooney.