LONDON — With Britain’s economy suffering a battering in recent days because of the country’s impending exit from the European Union, the United States sent a familiar face to offer assurance: White House national security adviser John Bolton.

At a briefing with British reporters on Monday evening, Bolton said Britain would be at the “front of the trade queue” for a new trade deal with the United States, adding that any agreement could be worked out “sector by sector” to speed up the process.

Bolton added that he and President Trump were “leavers before there were leavers” who supported Britain’s 2016 vote to end its membership in the E.U. His message from Trump was simple, he said: “We are with you.”

The U.S. official also criticized the European bloc’s treatment of its members’ citizens. “The fashion in the European Union when the people vote the wrong way from the way that the elites want to go is to make the peasants vote again and again until they get it right,” he said, according to the BBC.

Bolton earlier met with Prime Minister Boris Johnson at No. 10 Downing Street. He is the most senior Trump administration official to meet with Johnson since he took office in July.

Bolton was also set to meet Britain’s foreign secretary, defense secretary, Brexit secretary and international trade secretary during his two-day visit to the British capital.

Britain is expected to leave the E.U. on Oct. 31. But despite repeated attempts, the government has not been able to find support for an agreement on the terms of its exit.

Analysts say that a “no-deal” Brexit, in which Britain reverts to World Trade Organization rules on border controls, could be disastrous for the country, prompting huge delays at the borders and disrupting the economy.

In some areas, the disruption already may be showing. Britain’s Office for National Statistics announced last week that the country’s economy shrank for the first time since 2012, while the pound fell to a 10-year low against the euro. 

Bolton’s reassurances appeared likely to elicit a sigh of relief from Johnson, who has refused to rule out a no-deal Brexit amid a push against the E.U. for better terms. 

The U.S. official said that if the British government ultimately opted to leave the E.U. without a deal, “we would support it enthusiastically.” And he rejected the suggestion, made by President Barack Obama in 2016, that Britain would join the “back of the queue” for a new trade deal.

Bolton’s idea that trade agreements could be reached sector by sector, without the need for a single comprehensive deal first, is a concession that should make the lives of negotiators easier and speed up progress.

Although Bolton said that in some areas of trade, such as financial services, it may be hard to reach a deal, he expressed optimism that working in a “modular fashion” could yield progress. “In other words, you can carve out some areas where it might be possible to reach a bilateral agreement very quickly, very straightforwardly,” he said, according to the Guardian newspaper.

Although friendly, Bolton’s comments masked the often fraught relationship that the Trump administration has had with Britain. The U.S. leader is deeply unpopular with the British public, and his visits to Britain since becoming president have been accompanied by protests and controversy.

The British government is also at odds with the United States over key Trump administration policies, including those involving Iran and Huawei, a Chinese telecom giant under pressure from Washington.

Speaking on Monday, Bolton played down differences in policy and said he “fully understands” that Brexit is the British government’s main priority.

However, some former British officials worried that the Trump administration would ultimately drive a hard bargain in trade talks. 

“This is a highly transactional administration,” Jack Straw, who was foreign secretary in Tony Blair’s government, told BBC Radio 4’s “Today” program on Tuesday. “You don’t get something for nothing.”

Johnson is expected to have his first face-to-face meeting with Trump as prime minister later this month when the leaders of the Group of Seven economies meet in Chantilly, France. The two leaders spoke by phone on Monday.

Trump has spoken warmly of Johnson in the past, calling him a “good guy” and a “friend of mine” in remarks to reporters last month. “I think we’re going to have a great relationship,” he said in the Oval Office.

But Trump’s relationship with Theresa May, Johnson’s predecessor, also started out cordially. As she prepared to leave office last month, the U.S. president slammed her for not accepting his advice on Brexit, tweeting: “She went her own foolish way — was unable to get it done. A disaster!”