Amid flashing lights and pounding music, foreigners had their pick of drugs – marijuana, cocaine, ketamine, meth, fentanyl. Nightlife ran wild here for years in Xuzhou, a lush pocket of eastern China dotted with lakes and ringed by mountains.

“Back then we would go into clubs and just go table to table, drinking for free,” said one expat, declining to give a full name.

As few foreigners were willing to come for study or employment in this small city – accessible only by rail or road – expats said they were able to get away with this kind of freewheeling behaviour.

But a broad crackdown in China against corruption and crime has finally stretched from big cities like Shanghai to smaller locales like Xuzhou. And the authorities are emboldened to nab foreigners at a time of rising tensions between China and Western nations, including the US, UK and Canada.

“The ability and desire to catch foreign companies and foreigners operating illegally in China is higher now than it has ever been,” said Dan Harris, founder of Harris Bricken, a US-based law firm that specialises in China.

Last week, a group of 16 foreigners - thought to include four Britons - were arrested after a drug bust based on what Xuzhou police said was a tip. One is under criminal detention, which is typically followed by formal arrest and conviction – China’s murky courts, controlled by the ruling Communist Party, have a 99.9 per cent conviction rate.