Deputy Ambassador Thae Yong Ho stands in front of artwork at the North Korean Embassy in London in 2014. (Katie Schubauer/Agence France-Presse via Getty Images)

The second in command of North Korea’s embassy in London defected to South Korea with his family, officials in Seoul said Wednesday, describing him as “sick and tired” of Kim Jong Un’s regime.

The defection, the latest in a string of high-profile escapes, constitutes an embarrassing blow to North Korea’s authoritarian leadership and potentially an intelligence windfall for South Korea and its allies, including the United States.

Thae Yong Ho, a cosmopolitan career diplomat, was a key official at the embassy, in a residential area of west London, and is thought to have escorted Kim Jong Chul, the North Korean leader’s older brother, during his trip to Britain last year to attend an Eric Clapton concert.

“He is absolutely central to the operation of that embassy,” said Adam Cathcart, a North Korea expert at Leeds University who met Thae several times. “He’d been there longer than the ambassador, and all the North Korea hands in London assumed that he was a really key person there.”

Thae in some ways had been the public face of the embassy, giving talks at bookshops and at British Communist Party meetings in which he extolled the virtues of the North Korean system, a sign of the latitude he had within the regime, Cathcart said.

After several days of rumors, South Korea’s Unification Ministry confirmed Wednesday that Thae, who is thought to be in his late 50s, is now in Seoul with his family.

“They are now under the Seoul government’s protection, and relevant institutions are proceeding with necessary procedures,” Jeong Joon-hee, a ministry spokesman, told reporters, according to the Yonhap News Agency.

Defectors who held senior political or military positions within North Korea are extensively debriefed by the South Korean intelligence agency and then offered to U.S. military intelligence. They generally do not go through the resettlement program for regular defectors — where they learn things like how to use a credit card and the Internet — but often end up at a government-linked think tank.

The South Korean government, which has been taking a tough approach to North Korea since its nuclear test in January, used Thae’s escape to take another swipe at the regime in Pyongyang.

“This case shows that North Korean elites view that there is no hope in their country,” said Jeong of the Unification Ministry. “It also indicates that North Korea’s regime’s internal solidarity is weakening.”

But some analysts speculated that Thae’s departure could be linked to tougher sanctions against North Korea following this year’s nuclear and long-range missile tests. North Korea’s embassies are thought to be moneymaking centers, and over the years, diplomats have been caught smuggling contraband including gold, cigarettes, rhino horns and heroin. Increased scrutiny of North Korea’s activities, legal and otherwise, could make it harder for diplomats to meet their quotas.

South Korean officials did not disclose how or when Thae arrived, but the Guardian newspaper, quoting a student at his son’s school, suggested the family had “disappeared” sometime in July. Thae had talked publicly about living in London with his wife and said that his son attended high school in Acton, in west London. He has also mentioned an older son who graduated from a university with a degree in medicine or public health.

North Korean diplomats generally must leave one member of their immediate family in Pyongyang — the regime’s insurance against defections — and it was not clear whether Thae had managed to take all of his family with him.

Thae’s defection from London could complicate the delicate diplomatic ties between London and Pyongyang. A spokeswoman for the British Foreign Office said, “It’s not a story we’re commenting on.”

Thae was known in London for attending political and cultural events. At times, he seemed good-natured, even humorous, as he joked in English about the high cost of living in capitalist London.

Warwick Morris, a former British ambassador to South Korea who had met Thae on about four occasions, said the diplomat was “smooth and sophisticated in a slightly North Korean kind of way.”

But Thae also displayed the particular brand of public devotion to his government shown by North Korean diplomats. In 2014, for instance, he scolded British journalists during a speech at a London bookstore for allegedly exaggerating the security level at a major event in Pyongyang, comparing it to what reporters might face if they attended an event at Buckingham Palace.

“There has been so much ideological work by the ruling class of the British,” he said, according to a video of his speech posted on YouTube. He added that they have “brainwashed” the working class.

John Nilsson-Wright, head of the Asia program at Chatham House, a London-based think tank, said Thae was “very able, dapper, spoke excellent English ... He was atypical in a world of faceless bureaucrats and had a genuine interest in the country he was based in.

“I was surprised to learn of his defection, but not totally,” Nilsson-Wright said. “Anyone who is as bright as he is can see the difference between the official lines of the government and the reality of the outside world.”

Analysts agreed that Thae’s defection could be highly valuable to South Korea and the West. Thae would have come into contact, Nilsson-Wright said, with a number of influential people in the current North Korean administration. “He will have good details of how the government works,” he said.

North Korea allows only citizens deemed most loyal to the regime to travel abroad, so Thae’s flight marks the latest in a series of embarrassing defections.

In April, the South Koreans announced the arrival of a colonel from North Korea’s Reconnaissance General Bureau, the primary spy agency and the department believed to be behind the hacking of Sony Pictures in 2014 and the sinking of a South Korean naval corvette in 2010. That same month, South Korea confirmed the defection of 13 North Koreans working at a state-run restaurant in China — another key source of foreign currency for the regime.

Thae becomes the most senior North Korean diplomat to defect since the ambassador to Egypt sought asylum in the United States in 1997.

Karla Adam contributed to this report.