WASHINGTON — “Nothing in this room is off the record,” Juleanna Glover, a corporate consultant, warned the stragglers assembled in the kitchen of her Kalorama home as Steve Hilton, a former chief adviser to Prime Minister David Cameron of Britain, hunted for a beer.

It was the evening after Donald Trump had effectively sewn up the Republican nomination; the night’s conversations had been dominated by talk of polls and power.

Mr. Hilton is credited as the architect of a modernized British Conservative image — one that supports gay marriage, and countering climate change — that helped get Mr. Cameron elected. An outsider’s insider, in other words.

Mr. Hilton, and his ideas, had spent the week debuting here in Washington. Appearances were made at White House Correspondents’ Association dinner parties, on MSNBC’s “Morning Joe,” and at the American Enterprise Institute. Meetings were held with a who’s who of American conservatives, including Grover Norquist and Reince Priebus, the Republican National Committee chairman.

This final evening was a party for Mr. Hilton’s book, “More Human: Designing a World Where People Come First,” a call for smaller-scaled living and governance. (A British edition of the book received mixed reviews. It was largely revised for its American publication.)

The night had started five hours earlier.

Mr. Hilton, who has a closely shaved head, faintly bounced into the dining room. He was clad, as always, in a T-shirt (this one was black, festooned with white flecks that appeared, at a distance, to be stars), blue corduroys and red-striped white sneakers that bore the label Crowdpac — the nonpartisan political-crowd-funding site that Mr. Hilton founded with two partners.

On his wrist he wore a tattered aqua bracelet embroidered with the word “Coachella.” Four years ago, Mr. Hilton decamped London for California, where his wife, Rachel Whetstone, was the chief of public policy and communications for Google; she is now in the same position at Uber. (In contrast, Mr. Hilton is decidedly low-tech; he does not carry a cellphone.)

The room quickly filled with journalists, pollsters and think-tank pundits. A C-Span cameraman jostled for position.

“Such an illustrious crew — it reminds me of something,” Mr. Hilton said, as guests pressed up against a table laden with sushi. He began to read: “When the corporate bosses, the members of Congress, the journalists — and the authors of books like this — all go to the same dinner parties and galas and live in the same neighborhoods of Washington, New York and San Francisco, an insular ruling elite precipitates. … Regardless of who’s in office, the same people are in power.”

“It’s great to see you all here,” he deadpanned, looking up. The crowd laughed.

Mr. Hilton said that his book calls for radical change, from top-down government (more power to ultralocal, neighborhood government) to schools (no “factory schools,” a reconsideration of testing). A single social worker, for example, for a family in need.

It opens with an anecdote about a JetBlue flight trapped on the tarmac and regulations that required a mother to deny her young daughter the bathroom. Mr. Hilton, the son of Hungarians who fled Communism, invoked Hannah Arendt and inhuman systems, before turning to questions.

“Who are the enemies of your ideas?” Steve Clemons of The Atlantic asked.

Mr. Hilton spoke about decentralizing concentrations of power, including, perhaps, breaking up banks, health insurance, “giant agriculture” and telecom companies.

A British compatriot, Richard Reeves, who was the director of strategy for the former British Deputy Prime Minister (and Liberal Democrat) Nick Clegg, spoke up. “The people you want to give power to aren’t in the structure at the moment and don’t have a locus to bring about change,” he said.

Mr. Hilton vigorously agreed. The book, he said, calls for new blood in office. He segued into a pitch for Crowdpac, which allows for fund-raising “without depending on big party machinery which traps people in the existing power structures.”

Mr. Reeves, now at the Brookings Institution, said Mr. Hilton was “one of the most vibrant thinkers on the center right in British politics.” The book, he added, “authentically captures not just his political philosophy but his moral philosophy, which is that the bigness and centralized expertise of the modern state and the modern company is something he instinctively rebels against. He is hard to pin down politically.”

Standing near a stack of books for sale, Steve Schmidt, the Republican strategist and MSNBC commentator, recalled meeting Mr. Hilton in California when Mr. Hilton was looking at Arnold Schwarzenegger, “a fiscally conservative, socially tolerant and environmentally conscious” governor as a model for “how to rethink the right of center party in the U.K.”

Asked about Mr. Trump, Mr. Schmidt said that voters, “have turned to someone to be nominee for president with no government experience, no military experience, as an act of condemnation against the establishment.” It’s a line that echoes “More Human.” Mr. Hilton, he said, had a message of hope.

Tammy Haddad, a media strategist and one of the party’s co-hosts, arrived late, with a whoop of joy. She shook back her mane of black hair with its singular white stripe and swept Mr. Hilton into a hug.

Ms. Haddad, who consults for the HBO show “Veep,” barreled into a story about “The Thick of It,” the British precursor to “Veep.” “So you have to watch it — what happens is the whole season is an election, in the U.K.,” she said. The weekend before the voting, Ms. Haddad continued, the campaign manager of the winning candidate, a character reportedly inspired by Mr. Hilton, has everyone go to a yoga retreat. “And then I meet Steve and I’m like: “Oh, my God! It’s the guy. He’s exactly the guy.’”

Scott and Jason Bade, twins, and Mr. Hilton’s co-authors (he taught them as undergraduates at Stanford), protested. “He’s much more serious,” Scott said. Ms. Haddad looked over at them. “You’re not in politics,” she said. “It wasn’t goofy, it was the opposite. It was confidence.”

It was then that the final stragglers assembled in Ms. Glover’s kitchen. Around the marble center island were Heather Podesta, the lobbyist and art collector; Ms. Haddad; and Betsy Fischer Martin, a former producer of “Meet the Press.”

“To Steve, who is bringing the heart back into politics!” Ms. Haddad said. “And to being authentic.”

“Lovely,” Mr. Hilton said.

“Oh,” Ms. Haddad added, “and please subscribe. Betsy and I have a podcast.” The whole room laughed.

We are, Mr. Hilton noted, in America.