Seven people have been jailed for operating an undercover £55m money-laundering ring aimed at international university students seeking to bypass limits on the amount of cash that can be taken out of China.

Four people – three men and one woman – were sentenced at Snaresbrook crown court on Monday for a range of money-laundering offences. In June, three others were sentenced for similar offences. They were handed sentences ranging from 11 months to 12 years.

Chinese citizens cannot transfer more than $50,000 (£38,000) for personal purposes out of the country a year. To regulate this, citizens are required to process all transactions through a foreign exchange account opened with a Chinese bank account.

Some people circumvent the limit by using “underground banking”. A 2019 report from the National Crime Agency (NCA) said its use was probably “widespread among the Chinese diaspora in the UK”.

Officers in Stoke Newington, north London, found that £55m had been laundered among the group via Chinese underground banking between February 2020 and June 2023.

In December 2022, officers conducted two simultaneous warrants. While searching the first address, in London’s Canary Wharf, belonging to Xiaoyu Shu, 29, and Yin Ying Wang, 28, they found more than £104,000 in a carrier bag hidden in a wardrobe.

The second warrant took place at the address of Yunchen Huang, 28, where multiple cash counting machines and money bags were discovered. Officers seized a total of almost £500,000 in assets from the group.

Specialist officers discovered Shu and Huang were using a Chinese messaging app to sell British pounds to university students to bypass the foreign exchange limit. They also identified that Shu and Huang were working for a person who arranged for the pair to collect large amounts of cash, sometimes as large as £250,000 at a time.

The pair were not told the identities of those they collected cash from, and were instructed to take a photo of a £5 banknote, including the unique serial number. This was then passed on to the courier, allowing the interaction to take place without either party knowing the identity of the other, in order to prevent those in the chain giving information to police if they were arrested.

Officers also identified that Peng Liu, 28, and Ang Li, 26, also of Canary Wharf, were assisting the group by operating an unregistered money business. When officers searched their address in Canary Wharf in June 2023, they located counting machines and £14,600.

Officers were then able to identify that Qiji Wang, 29, who was based in Manchester, was the head of the group. When searching his address, they discovered numerous mobile phones, computers, bank cards in others’ names and a cash counting machine.

Ruolan Chen, 28, also based in Manchester, was also found to have assisted the group by operating an unregistered money service business.

DC Zach Rowe, of the Stoke Newington proactive crime team, said: “Thanks to the hard work and perseverance of highly skilled officers in the Met, we have been able to disrupt a sophisticated economic crime operation. The sheer scale of this laundering will generate crimes such as illegal drug supply, prostitution, human trafficking and more.

“This verdict, and the lengthy three-year investigation that led to it, demonstrates that we’ll leave no stone unturned in our pursuit to catch criminals who look to enjoy the proceeds of illicit funds – no matter how complex the case.”

Benn Maguire, lead counsel from the legal firm QEB Hollis Whiteman, said: “This successful prosecution has eviscerated the criminal operation, preventing those involved in crime from profiting from their wrongdoing.”