GETTY Thae Young Ho defected from North Korea after a trip to M&S

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Thae Young Ho, the son of a general linked to the founding of North Korea, had been stationed in London for more than 10 years before his defection, details of which read like a Graham Greene novel. Thae, a keen golfer who insisted on bringing his clubs when he boarded his last flight from England, made his first contact with British intelligence agents two months ago at a golf club in Watford.

According to sources, he revealed he had misgivings about returning to North Korean capital Pyonyang – a prospect that loomed in the near future. It was only when his wife Oh Sun Hae began to share the same sentiments that he began to consider the prospect seriously.

GETTY Mr Thae was based in London for 10 years

It took a fortnight before the Foreign Office informed American intelligence colleagues, time needed to assure themselves Thao was serious. Six weeks ago a small but elite multiagency group flew from Washington DC to London to plan his getaway. Despite the tightest security, it took only ten days for rumours of the defection to begin circulating in Seoul, South Korea that a defection was imminent “from somewhere in Europe”. Though given “carte blanche” to choose where in the world he wanted to base his family, the loyal Korean chose South Korea.

In the early hours of a mid-week day last month a small RAF BAe 146 aircraft, operated by the Royal Squadron, took off from Brize Norton in Oxfordshire. On board were Thae, his wife, and their two sons, aged 19 and 26, as well as seven additional British and American Foreign Office officials and secret service agents. The luggage included a set of tennis rackets owned by Mrs Thae, who had become a keen player since coming to England. Sources revealed that she had interrupted the journey to the airport with a request to make a stop at a Marks and Spencers containing a large food hall. “She was keen to stock up on her favourite treats before leaving the United Kingdom behind her,” said a senior source. The 30-seater aircraft took off in daylight hours, escorted by two Typhoon fighter jets, for the US Air Force base at Ramstein, in Germany. Thae’s youngest son Kum spent the two-hour flight penning a letter to a friend, in which he is said to have explained his disappearance since sitting his A-levels in double maths and computer science at school in Acton. He was due to begin studies for a degree at London University’s Imperial College next month.

GETTY Mr Thae defected to South Korea

His father, meanwhile, signed a latter of thanks he had previously began writing, which he asked to be hand-delivered to Theresa May. Once in Germany the family and some of the agents were transferred to another aircraft, bound for Seoul. Around 27,000 North Koreans have fled the totalitarian and impoverished state, bit of those very few have been high in the diplomatic chain. “It is clear that Mr Thae had been entertaining private concerns about his future, which was bound to include a return to Pyonyang,” a senior intelligence source told the Sunday Express last night. “Interestingly however, it was only when his wife began to share similar concerns that these thoughts took on a concrete form. “His defection represents an important intelligence coup."

GETTY Mrs Thae interrupted the journey back to South Korea to stock up on favourites from M&S

Mr Thae is expected to spend several weeks in “comfortable incarceration”, while South Korean intelligence agents ensure he is not a double agent. Last night experts warned that intelligence bosses responsible for preventing defections may be executed by a furious supreme leader Kim Jong un. "North Korea has a reputation for repercussions, such as executing those associated with a defector and using any means to retrieve those who dare to flee," said Dr John Nilsson-Wright, of the Chatham House think tank.