HSBC and Peter Lewis say they will both appeal against the findings of an employment tribunal in one of the first – and the biggest – cases to be brought under the 2003 sexual orientation regulations.

Peter Lewis, former head of HSBC’s global equity trading, brought a £5 million lawsuit against the bank after he was dismissed for gross misconduct – an allegation which he has always denied.

In the tribunal hearing, HSBC’s conduct was challenged on 16 points. The tribunal upheld Mr Lewis’ complaints on four of the points but found for HSBC on the remaining 12.

Now both parties are seeking leave to appeal against the findings. HSBC believes the tribunal went beyond its remit when it found faults with the bank’s initial handling of the case.

The tribunal criticised the HR executive who handled the initial investigation, saying she had been discriminatory. It felt that suspending Mr Lewis during the investigation was discriminatory and that the inclusion of a second allegation based on “flimsy” evidence and “hearsay” was also discriminatory.

But the tribunal found that the decision to dismiss Mr Lewis was based on the belief that he was guilty of gross misconduct and not on his sexual orientation.

But Mr Lewis says the allegation – of masturbating in a gym shower in front of another employee – would never have been believed had he been straight.

His lawyer, Alison Downie said he is challenging the ruling on the grounds that the disciplinary process that led to his dismissal was “tainted” by discrimination.