One of Britain's most prominent bankers Ian Hannam, who was dubbed the 'King of Mining' and 'JPMorgan's Rainmaker', told financiers at a London event that he appealed against a £450,000 fine for market abuse as "the rules were not very clear".
Speaking at the Financial Times's Camp Alphaville event, Hannam said the past four and a half years since regulatory claims were made against him have been difficult.
"It's safe to say I have had a lot of time to learn about what actually defines market abuse," said Hannam.
"From the period of 2009 to April 2012, I couldn't talk to anyone, to my wife to my employer, and when the regulatory decisions were made, I knew I had to fight it.
"I felt the rules [around market abuse] were not sufficiently clear."
At the end of May 2014, Hannam lost his appeal against the Financial Conduct Authority (FCA), previously the Financial Services Authority (FSA), after the markets watchdog gave him one of the largest ever fines imposed on an individual for market abuse in April 2012.
Britain's Upper Tribunal, which is a superior court presided over by three High Court judges, ruled against him and upheld the decision that Hannam was guilty of market abuse, even though his actions were unintentional.
However, all is not lost for Hannam. He has since set up his own advisory firm and has bought a factory in Germany for €206m ($281m, £164m).
Who is Ian Hannam?
'The King of Mining', Hannam led the flotations of Xstrata and Vedanta onto the London Stock Exchange and was pivotal in the merger between mining giants BHP and Billiton in 2001.
He also brokered some of the country's most high-profile deals, including the London listing of copper miner Kazakhmys.
He was also so powerful and famous at JPMorgan that his presence would immediately generate business, clients and money.
However, he stepped down after 12 years at JPMorgan after being hit with the fine to appeal the decision.
The FSA fined Hannam, the former Chairman of JPMorgan Cazenove's Capital Markets unit, after it ruled that he abused the market following two instances of what it called "improper disclosure".
This related to emails Hannam sent to a client in September and October of 2008 - the height of global financial crisis.
The FSA said the emails contained information about Heritage Oil, an Africa-focused exploration group and JPMorgan client, and potential bidding interest on the firm.
A second email contained privileged information about a new oil fund that Heritage was establishing at the time.
"Inside information is extremely valuable and must be handled with care to ensure that it is properly controlled and that appropriate safeguards are observed," said Tracey McDermott, acting FSA director of enforcement and financial crime, in a statement published at the time.
Hannam said in his appeal defence that no one traded on the information, his honesty was not questioned, he retained his "fit and proper" status, and he was acting in his client's interest in a manner appropriate for a financial adviser.