The nuclear armed dictatorship of North Korea is being governed by the brother-in-law of the country’s leader, Kim Jong Il, who succumbed to serious ill health three months ago, South Korean experts have concluded.

Government officials and academic North Korea watchers have received intelligence suggesting that Chang Sung Taek, a 62-year old who runs the totalitarian state’s secret police, is making key decisions while the “Dear Leader” convalesces.

They believe that Mr Kim is conscious and probably capable of walking, but that he remains weak after what appears to have been a sudden stroke suffered in the middle of August.

Despite the fact that Mr Kim has not formally named anyone to succeed him to the leadership of North Korea and its million-strong, nuclear-equipped army, the Government appears to be functioning normally for the time being with no obvious signs of instability.

“Chang Sung Taek is now in control and is leading North Korea,” said Choi Jin Wook, of the government-affiliated Korea Institute for National Unification in Seoul. “Other important figures consulted him, even when Kim Jong Il was OK. He will keep Kim Jong Il’s policy line even if he dies.”

Apart from his family connection to Mr Kim, Mr Chang is a cosmopolitan among North Korean cadres whose career bounced back from the brink of disaster just two years ago.

According to South Korea’s ministry of unification, he was educated at an elite school in Pyongyang, and married Mr Kim’s younger sister, Kim Kyong Hui, after studying in Moscow for three years.

He rose through the hierarchy to become head of the most powerful bureau of the Korean Workers’ Party’s, the “organisation and guidance department”. His older brother was the army general responsible for the defence of the capital itself.

In 2002, two years after a historic summit meeting between North and South, he led a delegation of senior officials on an unprecedented tour of South Korean industrial sites.

The most senior North Korean defector to the South, the former chief ideologue, Hwang Jang Yop, spoke of him as a potential successor to Mr Kim after a coup, and said that he was especially close to Kim Jong Nam, the dictator’s eldest son.

Perhaps because of his growing influence, Mr Chang was abruptly purged in 2004, and sent into internal exile. He reappeared in 2006 and last year a new and powerful post was created for him: head of the Party’s “administrative department”, in charge of the courts, the prosecutors, and the police – including those responsible for internal spying.

“He is very smart, dynamic, with maybe some charisma – that’s the image I have of him,” said Dr Choi. “He has fewer enemies [than other senior cadres] because when he purges people, they are not just sent away from Pyongyang, they are killed.”

Dr Choi declined to describe the source of the information about Mr Chang’s newly acquired position of power, which has been shared with him and other researchers and government officials, and it is impossible to verify independently.

Reading the internal politics of a regime as secretive and paranoid as that of North Korea has always been profoundly difficult, but rarely has it seemed so important since the sudden disappearance from the North Korean media of Mr Kim.

In the past he has sometimes disappeared from view for weeks on end, but when he failed to make an appearance at celebrations in September to mark the country’s 60th anniversary, Pyongyangologists around the world concluded that something was wrong.

Japanese television identified a French brain surgeon who had recently visited Pyongyang – although he denied having treated Mr Kim. The Government has angrily denied that anything is wrong with him, and has released several photographs of him attending public events, none of which have quelled the growing consensus that he is ill.

Photographs released last week showed signs of having digitally manipulated to insert the Dear Leader’s image into a crowd of soldiers.

But none of the governments which monitor North Korea most closely – South Korea, China and the US – have reported any signs of panic or unusual troop movements, suggesting that the government is coping with the indisposition of its leader.

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