China is still harassing dissidents who fled in the 1990s

Being in detention was not new to Yan. He had already spent 19 months in a Chinese prison for his part in 1989’s Tiananmen Square protests. Students had called for greater democracy and freedom, but the Communist Party sent in tanks to crush them.

At the end of June 1989, the Chinese government said that 200 civilians and several dozen security personnel had died. Other estimates have ranged from hundreds to many thousands.

On his release, Yan had made his way to southern China where, in scenes that could have been taken from a spy film, he was sent from one public phone booth to another, to be put in touch with the people who could get him out.

He was not the only dissident to undertake this risky journey.

Speaking to the BBC for a new series, Shadow War: China and the West, Chaohua Wang recalls her escape.

Despite being number 14 on a list of the 21 most wanted people after the Tiananmen Square protests, she managed to evade capture, hiding in tiny rooms for months before heading south and becoming part of the Yellow Bird escape line.

“I was like a parcel moved from one [person] to another,” she says.

“I didn’t even know the name Yellow Bird for quite some years.”

Yellow Bird may sound like a classic spy operation, and many believed that an intelligence service – MI6 or the CIA – had come up with the idea. But they had not.

In fact, it was a private enterprise undertaken by concerned groups of citizens in Hong Kong, motivated by a desire to help out those who were among the run. Among them were the local film and entertainment industry and (more usefully) organised crime, in the form of the triads.