Barclays boss Jes Staley will be probed by Britain's financial watchdog and have his pay docked over failings relating to the lender's whistleblowing programme.
The Financial Conduct Authority (FCA) and the Prudential Regulation Authority (PRA) have opened an investigation into Mr Staley's conduct and senior manager responsibilities after an attempt by Mr Staley to identify a Barclays whistleblower last year.
Following an independent investigation, Barclays has also decided to issue the chief executive with a formal written reprimand and ensure that a "very significant compensation adjustment" be made to Mr Staley's pay packet.
Barclays said that Mr Staley "honestly, but mistakenly, believed that it was permissible to identify the author" of a letter written by the whistleblower.
The board concluded that Mr Staley "made an error" in becoming involved with and not applying appropriate governance around the matter.
Mr Staley has apologised to the board, but will nevertheless see his pay docked, with the precise amount of the compensation adjustment to be determined once the FCA and PRA investigations have concluded.
The bank is also commissioning independent reviews of its processes and controls, including its whistleblowing programme.
Barclays and Mr Staley will co-operate fully with the FCA and PRA investigations, the bank said.
Mr Staley said: "I have apologised to the Barclays board and accepted its conclusion that my personal actions in this matter were errors on my part.
"I will also accept whatever sanction it deems appropriate. I will co-operate fully with the Financial Conduct Authority and the Prudential Regulation Authority, which are now both examining this matter.
"Our whistleblowing process is one of the most important means by which we protect our culture and values at Barclays and I certainly want to ensure that all colleagues, and others who may utilise it, understand the criticality which I attach to it."
The incident refers to anonymous letters sent in 2016 to the board and a senior executive which raised concerns about a newly-recruited senior employee.
The letters raised concerns of a personal nature about the senior employee and Mr Staley's role in the recruitment.
Having been given a copy of the first letter and made aware of the second, Mr Staley initially requested that Barclays Group Information Security team attempt to identify the authors of the letters.
Mr Staley considered that the letters were an unfair personal attack on the senior employee, the bank said.
The attempt to uncover the whistleblower's identity was ultimately unsuccessful.
Barclays chairman John McFarlane said: "I am personally very disappointed and apologetic that this situation has occurred, particularly as we strive to operate to the highest possible ethical standards.
"The board takes Barclays' culture and the integrity of its controls extremely seriously.
"We have investigated this matter fully using an external law firm and we will be commissioning an independent review of Barclays' processes and controls to determine what improvements may be required."
"The board has concluded that Jes Staley... honestly, but mistakenly, believed that it was permissible to identify the author of the letter and has accepted his explanation that he was trying to protect a colleague who had experienced personal difficulties in the past from what he believed to be an unfair attack, and has accepted his apology."
Mr McFarlane added that Mr Staley has an otherwise exemplary record and continues to have the board's unanimous confidence and support.