Tonight's glamorous White House State Dinner brought Hollywood celebrities, political financiers and Washington power players together to celebrate the relationship between the U.S. and Britain.

The election-year State Dinner was the largest hosted by the Obama administration yet, with 300-plus guests. Among those invited to the soiree were actor George Clooney, who scored a seat next to the First Lady, Vogue editor Anna Wintour, actor Idris Elba, and Sir Richard Branson.

Billionaire Warren Buffett, movie producer Harvey Weinstein, Rory McIlroy, the no. 1  golfer in the world, and stars of the hit show "Downton Abbey" also made the list.

Move than 40 of Obama's top campaign financiers were in attendance.

In short opening toasts, President Obama and British Prime Minister David Cameron underscored the strength of their "essential" political alliance and close personal relationship.

"In good times and in bad, he's just the kind of partner that you want at your side. I trust him. He says what he does, and he does what he says. And I've seen his character," Obama said of Cameron.

Both leaders also brought some humor to the dinner. Cameron threatened to expose what really happened on their "guys night out." Obama treated Cameron to an NCAA tournament game in Ohio Tuesday night.

"Maybe I should come clean about last night. We went to basketball and we had a real man-to-man chat. Barack tried to confuse me by talking about bracketology but I got my own back by running him gently through the rules of cricket," Cameron said to laughter from the crowd.

On a more serious note, the prime minster gave a glowing endorsement of the president's leadership abroad. "He has pressed the reset button on the moral authority of the entire free world," he said. "Barack has not rushed into picking fights, but is a steward of America's resources of hard and soft power… He's taken time to make considered decisions, drawing down troops from Iraq and surging in Afghanistan. He's found a new voice for America with the Arab people. "

Guests were treated to a "backyard celebration," dining in a gigantic white tent set up on the South Lawn for the occasion. Attendees feasted on shaved Brussels sprouts, bison wellington, and steamed lemon pudding all prepared with ingredients from the White House kitchen garden's winter harvest.

The atmosphere at tonight's dinner was one of pure elegance and glitz. The tent was lit in purple hues and the space was decorated with lush green, purple and pink blossoms. Tables of various shapes were adorned with purple and silver tablecloths in modern prints and tall dramatic centerpieces.

While purple and green were the colors of tonight's décor, blue dominated the fashion. Mrs. Obama and Mrs. Cameron both wore floor-length blue gowns. The first lady donned a teal blue off-the-shoulder Marchesa gown designed by Georgina Chapman, who was a guest tonight and lives between the U.S. and the U.K.

Mrs. Cameron wore a sparkling dark blue lace gown with elbow-length sleeves.

"They look better than us," the president, dressed in a basic tuxedo, was overhead saying as the Camerons arrived at the White House this evening.