The old habits of secrecy haven't left Kim Kuk-song.

It has taken weeks of discussions to get an interview with him, and he's still worried about who might be listening. He wears dark glasses for the camera, and only two of our team know what we think is his real name.

Mr Kim spent 30 years working his way to the top ranks of North Korea's powerful spy agencies. The agencies were the "eyes, ears, and brains of the Supreme Leader", he says.

He claims he kept their secrets, sent assassins to kill their critics, and even built an illegal drugs-lab to help raise "revolutionary" funds.

Now, the former senior colonel has decided to tell his story to the BBC. It's the first time such a senior military officer from Pyongyang has given an interview to a major broadcaster.

Mr Kim was the "reddest of the red", he says in an exclusive interview. A loyal communist servant.

But rank and loyalty do not guarantee your safety in North Korea.

He had to flee for his life in 2014, and since then he has been living in Seoul and working for South Korean intelligence.

He depicts a North Korean leadership desperate to make cash by any means possible, from drug deals to weapons sales in the Middle East and Africa. He told us about the strategy behind decisions being made in Pyongyang, the regime's attacks on South Korea, and claims that the secretive country's spy and cyber networks can reach around the world.

The BBC cannot independently verify his claims, but we have managed to verify his identity and, where possible, found corroborating evidence for his allegations.

We contacted the North Korean embassy in London and the mission in New York for a statement, but have so far received no response.
A 'terror task force'

Mr Kim's last few years in North Korea's top intelligence unit offer some insight into the early career of the current leader, Kim Jong-un. He paints a picture of a young man eager to prove himself as a "warrior".

North Korea formed a new spy agency called the Reconnaissance General Bureau in 2009, just as Kim Jong-un was being groomed to succeed his father, who had suffered a stroke. Chief of the bureau was Kim Yong-chol, who remains one of the North Korean leader's most trusted aides.

The colonel said that in May 2009, an order came down the chain of command to form a "terror task force" to kill a former North Korean official who had defected to the South.

"For Kim Jong-un, it was an act to satisfy the supreme leader (his father)," Mr Kim says.

"A 'Terror Force' was formed to assassinate Hwang Jang-yop in secret. I personally directed and carried out the work."

Hwang Jang-yop was once one of the country's most powerful officials. He had been a key architect of North Korean policy. His defection to the South in 1997 had never been forgiven. Once in Seoul, he was extremely critical of the regime, and the Kim family wanted revenge.

But the assassination attempt went wrong. Two North Korean army majors are still serving 10 year prison sentences in Seoul for the plot. Pyongyang always denied it was involved and claimed South Korea had staged the attempt.

Mr Kim's testimony would suggest otherwise.

"In North Korea, terrorism is a political tool that protects the highest dignity of Kim Jong-il and Kim Jong-un", he says. "It was a gift to demonstrate the successor's loyalty to his great leader."

There was more to come. A year later, in 2010, a South Korean navy ship, the Cheonan, sank after being hit by a torpedo. Forty-six lives were lost. Pyongyang has always denied its involvement.

Then, in November that year, dozens of North Korean artillery shells hit the South Korean island of Yeongpyeong. Two soldiers and two civilians were killed.

There has been much debate over who gave the order for that attack. Mr Kim said he was "not directly involved in the operations on the Cheonan or Yeonpyeong Island", but they "were not a secret to RGB officers, it was treated with pride, something to boast about".

And those operations would not have happened without orders from the top, he says.

"In North Korea, even when a road is built, it cannot be done without the direct approval of the Supreme Leader. The sinking of the Cheonan and the shelling of Yeongpyeong Island are not a thing that could be carried out by subordinates.

"This kind of military work is designed and implemented by Kim Jong-un's special orders. It's an achievement."
'Spy in the Blue House'

Mr Kim says one of his responsibilities in the North was developing strategies to deal with South Korea. The aim was "political subordination".

That involved having eyes and ears on the ground.

"There are many cases where I directed spies to go to South Korea and performed operative missions through them. Many cases", he claims.

He doesn't elaborate, but he does give us one intriguing example.

"There was a case where a North Korean agent was dispatched and worked at the Presidential Office in South Korea and returned to North Korea safely. That was in the early 1990s. After working for the Blue House (South Korea's Presidential Office) for five to six years, he came back safely and worked at the 314 Liaison Office of the Labor Party.

"I can tell you that North Korean operatives are playing an active role in various civil society organisations as well as important institutions in South Korea."

The BBC has no way of verifying this claim.

I have met several convicted North Korean spies in South Korea, and, as NK News founder Chad O'Carroll notes in a recent article, South Korean prisons were once filled with dozens of North Korean spies arrested over the decades for various types of espionage work.

A handful of incidents have continued to occur and at least one involved a spy sent directly from the North. But NK News data suggests that far fewer people have been arrested in South Korea for spy-related offences since 2017, as the North turns to new technologies, rather than old fashioned spies, for intelligence gathering.

North Korea may be one of the world's poorest and most isolated countries, but previous high-profile defectors have warned that Pyongyang has created an army of 6,000 skilled hackers.

According to Mr Kim, the previous North Korean leader, Kim Jong-il, ordered the training of new personnel in the 1980s "to prepare for cyberwarfare".

"The Moranbong University would pick the brightest students from all over the country and put them through six years of special education," he says.

British security officials believe that a North Korean unit known as the Lazarus Group was behind a cyber-attack that crippled parts of the NHS and other organisations around the world in 2017. The same group is believed to have targeted Sony Pictures in a high-profile hack in 2014.

Mr Kim says the office was known as the 414 Liaison Office.

"Internally, we dubbed it "Kim Jong-il's Information Centre."

He claims it had a direct telephone line to the North Korean leader.

"People say these agents are in China, Russia, and Southeast Asian countries, but they also operate in North Korea itself. The office also safeguards communication between North Korean spy agents."
Drugs for dollars

Kim Jong-un has recently announced the country is once again facing a "crisis" and in April he called on his people to prepare for another "arduous march" - a phrase that has come to describe a disastrous famine in the 1990s, under Kim Jong-il.

Back then, Mr Kim was in the Operations Department and was ordered to raise "revolutionary funds" for the Supreme Leader. That, he says, meant dealing in illegal drugs.

"The production of drugs in Kim Jong-il's North Korea peaked during the Arduous March," he says. "At that time, the Operational Department ran out of revolutionary funds for the Supreme Leader.

"After being assigned to the task, I brought three foreigners from abroad into North Korea, built a production base in the training centre of the 715 liaison office of the Workers' Party, and produced drugs.

"It was ICE (crystal meth). Then we could cash it to dollars to present to Kim Jong-il."

His account of drug dealing at this time is plausible. North Korea has a long history of drug production - mostly heroin and opium. A former North Korean diplomat to the UK, Thae Yong-ho, who also defected, told the Oslo Freedom Forum in 2019 that the country had engaged in state-sponsored drug trafficking and was trying to fix a widespread domestic drug addiction epidemic.

I ask Mr Kim where the drug money went. Was it converted into cash for the people?

"To help you understand, all the money in North Korea belongs to the North Korean leader," he says. " With that money, he'd build villas, buy cars, buy food, get clothes and enjoy luxuries."

Estimates of the death toll from North Korea's prolonged food shortages in the 1990s range from hundreds of thousands to up to a million people.
North Korean woman collecting grass to eat in a field, North Hamgyong Province, Jung Pyong Ri, North Korea on May 7, 2010 in Jung Pyong Ri, North Korea.

Another source of income, according to Mr Kim, came from illegal weapons sales to Iran, managed by the Operations Department.

"There were special midget-submarines, semi-submersibles. North Korea was very good at building cutting edge equipment like this," he says.

This may be a bit of North Korean propaganda as the country's submarines have noisy, diesel engines.

But Mr Kim claims that the deals were so successful that North Korea's deputy director in Iran would boast about summoning the Iranians to his swimming pool to do business.

North Korean weapons deals with Iran have been an open secret since the 1980s and even included ballistic missiles, according to Professor Andrei Lankov, one of the world's leading authorities on North Korea.

North Korea has continued to advance the development of weapons of mass destruction, despite being subject to strict international sanctions. In September, the country tested four new weapons systems including a new long-range cruise missile, a train-launch system for a ballistic missile, a hypersonic missile, and an anti-aircraft missile.

The technology is growing ever more sophisticated.

According to Mr Kim, Pyongyang also sold weapons and technology to countries fighting long civil wars. In recent years, the United Nations has accused North Korea of supplying arms to Syria, Myanmar, Libya and Sudan.

The UN warns that weapons developed in Pyongyang could end up in many troubled corners of the world.
'A loyal servant betrayed'

Mr Kim led a privileged life in North Korea. He claims he was given use of a Mercedes-Benz car by Kim Jong-un's aunt, and allowed to travel abroad freely to raise money for the North Korean leader. He says he sold rare metals and coal to raise millions in cash, which would be brought back into the country in a suitcase.

In an impoverished country where millions of people are struggling with food shortages, this is a life few can imagine, let alone live.

Mr Kim's powerful political connections through marriage allowed him to move between different intelligence agencies, he says. But those same connections also put him and his family in danger.

Not long after ascending to the political throne in 2011, Kim Jong-un decided to purge those he perceived as a threat, including his own uncle, Jang Song-thaek. There had long been suggestions that Mr Jang was the de-facto leader of North Korea, as Kim Jong-il's health faded.

According to Mr Kim, Jang Song-thaek's name had become more widespread than Kim Jong-un's.

"That's when I felt Jang Song-thaek wouldn't last long. I felt he would be banished to the countryside," he says.

But then North Korean state media announced in December 2013 that Mr Jang had been executed.

"I was more than surprised, it was a fatal blow and I was appalled," Mr Kim says. "I immediately felt a danger to my life. I knew I could no longer exist in North Korea."

Mr Kim was abroad when he read about the execution in a newspaper. He decided to make a plan to flee with his family to South Korea.

"To abandon my country, where my ancestor's grave and family is, and to escape to South Korea, which at the time for me was a foreign land, was the worst grief-stricken decision of emotional distress," he says.

Even behind his dark glasses, I can see that the memory is difficult for him.

The one question I keep asking during our many meetings, over many hours, was why he decided to speak now.

"This is the only duty that I can do," he says. "I'll be more active from now on to free my Northern brethren from the grasps of dictatorship and for them to enjoy true freedom."

There are more than 30,000 defectors in South Korea. Only a few decide to speak to the media. The more high profile you are, the higher the risk to you and your family.

There are also many in South Korea who doubt defectors' accounts of their lives. After all, how can anyone truly verify their stories?

Mr Kim lived a highly unusual life. His account should be read as part of North Korea's story - not the whole. But his story offers us a view inside a regime few are able to escape, and tells us something about what it takes for the regime to survive.

"North Korea's political society, their judgement, their thought processes, they all follow the conviction of ultimate obedience to the Supreme Leader," he says. Over generations, it produces a "loyal heart".

The timing of this interview is also interesting. Kim Jong-un has hinted he may be willing to talk to South Korea in the near future, if certain conditions are met.

But here too, Mr Kim offers a warning.

"It's been years since I came here, but North Korea hasn't changed at all," he says.

"The strategy we set up continues. What you need to know is that North Korea hasn't changed 0.01%."