Barclays's head of internal security is to be investigated by the bank's board over the whistle-blower scandal that has engulfed its chief executive Jes Staley, according to reports.

The BBC says Troels Oerting assisted Staley in his attempts to unmask the author of an anonymous letter that was sent to the bank last year.

The letter reportedly raised questions about the past conduct of Tim Main, a senior employee who was hired by Barclays in early 2016.

Main was a former colleague of Staley, with the pair having worked together for many years at US investment bank JP Morgan.

Staley has been formally reprimanded for his actions by Barclays and is likely to be hit with a financial penalty in excess of £1m ($1.3m).

The Bank of England's Prudential Regulation Authority and the Financial Conduct Authority have also opened their own investigations into the whistleblower case, along with New York's Department of Financial Services.

In a statement released on 10 April, Barclays said Staley, 60, had "honestly, but mistakenly, believed that it was permissible to identify the author of the letter".

In an internal letter to staff seen by the Guardian newspaper, Staley explained that he got personally involved in the matter as he believed that Mann was being "maliciously smeared".

"One of our colleagues was the subject of an unfair personal attack sent via anonymous letters addressed to members of the board and a senior executive at Barclays," the letter reportedly said.

"The allegations related to personal issues from many years ago, and the intent of the correspondents in airing all of this was, in my view, to maliciously smear this person.

"My hope was that if we found out who was sending these letters we could try and get them to stop the harassment of a person who did not deserve that treatment.

"Nevertheless, I realise that I should simply have the compliance function handle this matter, as they were doing. This was a mistake on my part and I apologise for it."