Night had fallen as Simon Cheng Man-kit, a UK consulate employee, rushed to catch a train home to Hong Kong. He’d spent the day on a business trip in southern China and was looking forward to an evening off.

But he was nervous about the trip back – for weeks, border officials had stepped up checks, questioning people travelling to and from Hong Kong, where anti-government protests were roiling the city.

So he stayed in constant contact with friends and family, letting them know he was safe, even messaging his girlfriend from the station: “Passing through. Pray for me.”

That was the last anyone would hear from Mr Cheng, 29, a trade and investment officer, as he disappeared into the Chinese state for more than two weeks.

During this time he was subjected to physical torture, psychological intimidation, political indoctrination and repeated interrogations by state security agents, sometimes by teams of 15 men.

Authorities called him an enemy of the state for working for the UK, threatened to charge him with subversion and espionage, and demanded he admit the British government was masterminding the protests in a direct challenge to China.