By Clara Ferreira-Marques

LONDON (Reuters) - The battle by one of London's most prominent bankers to overturn a fine for market abuse nears the end on Thursday, as lawyers wrap up a case that has prompted debate over banks' working practices and tested Britain's new financial regulator.

Ian Hannam has been a high-profile name in London financial circles for more than a decade. Once a so-called rainmaker at investment bank JP Morgan, he brought in clients, money and respect thanks to his bulging contact book.

But the former soldier, dubbed "king of mining" because of his weight in the resources sector, fell foul of the regulator and was fined 450,000 pounds ($730,000) last year. That was one of the highest penalties levied in Britain against an individual.

He quit his job as chairman of capital markets at JP Morgan to clear his name and is seeking to restore his reputation with an appeal against the fine that began in July.

Lawyers on both sides will present concluding arguments on Thursday before the judge-led Upper Tribunal retires to consider its decision, a process that could take months.

Even if the tribunal backs the Financial Conduct Authority (FCA), the regulator which replaced Britain's Financial Services Authority (FSA) earlier this year, the judges will still have to decide if a fine is warranted, and if so how much.

Hannam was accused in 2012 by the then FSA of sending two emails in 2008 on behalf of a client, Heritage Oil, which included what the regulator considered "inside" or market-moving information. The emails, out of a batch of 20,000, were pored over after Hannam himself blew the whistle on an unrelated insider trade.

No-one traded on the information in Hannam's emails and the regulator did not remove his "fit and proper" status, required for working in London's financial sector. But the regulator, which has sought to make an example of a banking heavyweight, has accused Hannam of having a "relaxed and improper attitude to confidentiality".

Hannam, who was disciplined by JP Morgan in 2009 around the time the FSA began its investigation, denies the statements in the emails constituted inside information and argues that the disclosures were made in the course of his work and for the benefit of the client.

Partly due to Hannam's candid admissions during questioning, that argument has fuelled debate over what should count as inside information and what is legitimate for a banker to do and say.

"I either made it up or I was putting a spin on it to get a meeting (with the minister)," Hannam told the tribunal in July of takeover talks revealed to a Kurdish minister in one of the 2008 emails. "I know everything I was doing was to further the transaction."

His appeal is also a high-profile test for the FCA's tactic of targeting big names to fight market abuse, following the strategy of U.S. watchdogs.

Rebuilding his reputation is critical for Hannam, who is building up a gold venture in Afghanistan and an advisory firm Strand Partners, which includes some of the JP Morgan team who were among the most influential in the sector.

(Reporting by Clara Ferreira-Marques; Editing by Erica Billingham)