Darren Flood, 39, who was married to Victoria Beckham's sister Louise Adams, was allegedly part of a boiler room fraud which tricked people into "worthless" investments.
The company focused on "high net worth clients" and discussed potential targets including former Chelsea footballer Joe Cole's father, it is alleged.
A jury at Kingston Crown Court was told staff "made great play on Darren Flood being David Beckham's brother-in-law" to win the trust of investors.
But Flood was accused by colleagues at the company, The Commodities Link, of not performing on any level other than to extract expenses, the court heard.
Victims were allegedly encouraged to buy "rare earth" substances, which are mainly used to make tech products, with the promise of big profits.
They invested more than £800,000 between April 2012 and August 2014 - but the materials had no resale value, prosecutor Stephen Shay said.
Flood was tasked with targeting potential high net worth investors, who paid up to 200 times over the odds for baskets of materials, the jury heard.
Mr Shay said one company salesman, Paul Muldoon, used the false name Paul Roberts to con thousands of pounds from victims.
He told jurors: "Paul Roberts stresses his experience and that of other brokers, even though the company, TCL, had only just been set up.
"He, Paul Roberts, made great play of Darren Flood being David Beckham's brother-in-law, which was the position, I think, at one point in the past."
Muldoon pleaded guilty to fraud by false representation at an earlier hearing.
Referring to the bogus investments, Mr Shay added: "There is no resale market for rare earth elements in this format or quantity.
"Manufacturers buy directly from suppliers by the ton. They would never seek to purchase a few kilograms from a private individual."
The jury was told rare earth materials gained publicity in 2010, two years before the alleged fraud, because the main supplier, China, "restricted global exports, causing a spike in the price."
But when The Commodities Link began trading in 2012, prices were falling as buyers searched for cheaper alternatives.
Victims of the company paid "between seven and 200 times" over the odds, Mr Shay said.
Flood was a director of the company between June 2012 and April 2013 - but documents uncovered by detectives revealed tensions with colleagues, Mr Shay said.
One titled "TCL requirements", which was read to the jury, said: “Jonny and Darren need to talk with high net worth clients, people, potential customers that you know.
"Since June we have been talking about Joe Cole's dad."
The document, which was meant for co-defendant Jonathan Docker, said the company's "output is terrible".
It stated: "The politics between you and Darren must be sorted.
"The business is on its knees over where leads get sent. That is f***ing ridiculous."
Mr Shay said: "That document would appear to suggest Darren Flood and Jonny Docker were not getting on particularly well while TCL was in operation."
The document went on: "Darren has not performed on any level other than to charge money to the business and extract expenses.
"He got a bank account but this could have been done with any high street bank.
"Darren threatens to leave and close the bank accounts. This is a common threat and makes progressing the business very difficult."
The Commodities Link was wound up by the High Court on 29 August 2014, Mr Shay said.
Flood and four others deny one count of fraud by false representation after claiming "rare earth elements were a suitable investment product".
The others are Gennaro Fiorentino, 38, Jonathan Docker, 32, Mark Whitehead, 59, and Vikki King, 39.
Paul Muldoon, 34, has pleaded guilty to the same charge at an earlier hearing.
Tarun Jain, 49, Ike Obiamiwe, 56, and Daniel Jordan, 35, deny laundering earnings from the alleged fraud.
The trial continues.
