LONDON (Bloomberg) — A former senior banker at HSBC Holdings Plc lost his appeal of a gay discrimination case against the lender, in the largest UK lawsuit of its kind.

Peter Lewis, HSBC’s former global head of equities trading, brought a $5 million ($9.8 million) claim after he was fired in 2004 for allegedly sexually harassing a male colleague. The Employment Appeal Tribunal in London yesterday ruled the openly gay banker wasn’t dismissed because of his sexual orientation, backing an earlier ruling.

The tribunal also overturned findings HSBC discriminated against Lewis during its initial investigation of the harassment complaint, saying the employment panel that first heard the case drew “unfair” conclusions that weren’t argued. That part of the claim will be sent to a new tribunal for a rehearing.

“HSBC has always maintained that Mr. Lewis was dismissed for gross misconduct following a complaint of sexual harassment made against him by another member of staff and for no other reason,” spokesman Pierre Goad said in a statement.

The case was the biggest gay discrimination claim brought to an employment tribunal in Britain, and the first by a high- profile financial executive. Lewis filed the lawsuit after he was fired by HSBC in December 2004, when a male colleague complained that he saw him masturbate in the health club of the bank’s London headquarters.

Lewis, who also formerly worked at French lender Societe Generale SA, denies the incident occurred and claims HSBC failed to properly investigate the allegations because of his sexual orientation.

An east London employment tribunal rejected his central claim that he was fired because he is gay in May. However, the same panel backed four of his 16 discrimination allegations, ruling that the HSBC human resources professional that led the investigation of the gym complaint, Natalie Hattrell, “embellished and exaggerated” her report and suppressed details that may have been favourable to Lewis.

The Employment Appeal Tribunal reversed those findings, saying that Hattrell’s honesty during the investigation wasn’t part of Lewis’s case. The tribunal also said the lower panel failed to consider whether she may have “subconsciously” discriminated against Lewis, having known he was gay.