London staff at BGC Partners have been accused by the Wall Street broker of stealing $35m (£24.7m) to spend on property and jewellery.
Michael Viney and Xavier Alcan allegedly funnelled cash due to or from HMRC to themselves between 2015 and 2020, according to a UK court filing seen by the Financial Times.
BGC, which acts as an intermediary between investment banks, disclosed the alleged fraud in February but did not provide any further details about the case.
However, the civil lawsuit claims that Mr Alcan, a senior BGC broker, encouraged tax adviser Mr Viney to facilitate the frauds.
It claims that the pair used the proceeds from the alleged fraud to splash out on expensive goods, including Cartier and Bvlgari jewellery and a £1.2m property in St Albans for Mr Viney's girlfriend.
BGC declined to comment. Taylor Wessing, Mr Alcan's law firm, did not respond to a request for comment. Mr Viney's law firm, Enyo Law, did not respond to a request for comment.
Mr Viney and Mr Alcan are accused of diverting funds owed to BGC by HMRC to an account controlled by Mr Alcan after telling the tax authority that Mr Alcan was authorised to receive the money on behalf of the broker.
Mr Viney also allegedly diverted £12.6m of payments owed to HMRC by BGC to himself and Mr Alcan. He is accused of using doctored documents that replaced bank details for the tax authority with their own.
The court filing claims the pair have been suspended from BGC.