A City trader has been jailed for two-and-a-half years after making £3m-worth of unauthorised trades.
Jonathan Bunn's deals brought Lewis Charles Securities "to its knees" and led to 12 people being made redundant and 20% pay cuts for staff.
The 31-year-old was jailed at Southwark Crown Court after admitting to false accounting between 22 and 24 July 2009.
Bunn, of Weybridge, Surrey, was banned from working in the finance industry by the Financial Services Authority.
The former inter-deal broker took up a short position equal to 6.95 million shares in HSBC and then lied by saying he had hedged the trades, the court heard.
He made £500,000 for Lewis Charles Securities (LCS) and £300,000 commission for himself within five months of joining the firm.
He thought the HSBC shares were overpriced and speculated on the price dropping, but when the prices "went up and up and up" his gamble "spiralled out of control", the court heard.
He also filled in four deal slips to hide the trades which had gone wrong.
David Levy, for prosecution, said Bunn's trades led to losses of £2,557,026 and a further £322,000 in associated costs.
Sentencing Judge Geoffrey Rivlin, the Honorary Recorder of Westminster, said: "You were not stealing your company's money but you were gambling with it in a very reckless and dishonest manner.
"I think I can fairly say that as a result of your very serious misconduct you have certainly made a very significant contribution to bringing this company, at least temporarily, to its knees."
Twelve staff members were laid off and everybody had to accept a 20% salary cut to keep the firm in business. The case also harmed LCS's reputation leading to loss of contracts.
Gregory Fishwick, defending Bunn, said the "greed" of the commission made him take the gamble.
"What started off as a much smaller offence grew beyond his control."
The court heard Bunn was a gambler and owed £60,000 to an online spread-betting company.