A woman has been convicted for her role in a multibillion-pound bitcoin fraud after what is thought to have been the world’s largest cryptocurrency seizure.

Zhimin Qian, also known as Yadi Zhang, 45, orchestrated a fraud in China between 2014 and 2017 that left 128,000 people out of pocket.

She stored the proceeds in bitcoin, but UK authorities made a breakthrough in the case when they raided a Hampstead mansion in 2018 and seized devices from Qian holding 61,000 bitcoins, worth more than £5bn at current prices.

The Metropolitan police believe it is the largest single cryptocurrency seizure in the world.

Qian pleaded guilty at Southwark crown court on Monday to acquiring cryptocurrency that was criminal property and possessing it between October 2017 and April 2024.

She had fled China using a bogus St Kitts and Nevis passport in 2017 and entered the UK, where a year later she attempted to launder the money by buying property with the help of Jian Wen, 43, a Chinese takeaway worker. Wen was jailed for six years and eight months for her part in the scam in May 2024.

Qian appeared in court aided by a Mandarin interpreter. She will be sentenced at a later date.

Wen had arrived in the UK in 2007 and lived modestly in Leeds between 2011 and 2017 before working at a Chinese takeaway in south-east London. She moved in with Qian at a six-bedroom house in Hampstead Heath, north London, in September 2017.

While laundering the proceeds of the fraud, Wen drove around in a Mercedes and flew her son over from China 18 months later to attend a private school.

Qian fled after police raided the Hamsptead property, known as the Manor House, and seized a safety deposit box containing digital wallets that held vast sums in bitcoin.

Wen insisted she had no idea that the bitcoin came from the proceeds of fraud and claimed Qian had duped her. She said she helped Qian run a jewellery business which had branches in Singapore, Malaysia and China.

In January this year a judge ordered Wen to pay back more than £3m with three months or serve another seven years in jail. The recoverable amount derived from the bitcoin and two properties in Dubai.

The head of the Met’s economic and cybercrime command, Will Lyne, said: “This is one of the largest money laundering cases in UK history and among the highest-value cryptocurrency cases globally. I am extremely proud of the team.

“Through a meticulous investigation and unprecedented cooperation with Chinese law enforcement, we were able to obtain compelling evidence of the criminal origins of the cryptoassets Qian attempted to launder in the UK … My thoughts are with the thousands of victims defrauded in this scheme.”

DS Isabella Grotto, who led the Met’s investigation, said: “Today marks the result of years of painstaking work. When our team located Zhimin Qian, she had been evading justice for five years, and her arrest triggered a complex investigation requiring evidence from multiple jurisdictions and the careful review of thousands of documents.

“I am immensely proud of the investigation team and our partners who have worked tirelessly on this case.”