Barclays Bank and its chief executive are being investigated by regulators over their handling of concerns raised by a whistleblower.
The bank made the information public while disclosing to the stock market that it had issued a formal reprimand and would impose a "very significant compensation adjustment" on Jes Staley.
It said the bank's board imposed the measures after an independent investigation into his attempts to identify a whistleblower who had raised, in two letters, concerns about a recently recruited senior member of staff.
Mr Staley said in a memo to more than 120,000 staff that he "got too personally involved" in the matter after what he saw as an "unfair personal attack" against the colleague.
Barclays said the anonymous letters highlighted issues of a "personal nature" and also raised worries about Mr Staley's knowledge of, and role in, dealing with those issues at a previous employer.
Its statement said: "The investigation by Simmons & Simmons LLP found, and the board has concluded, that Mr Staley honestly, but mistakenly, believed that it was permissible to identify the author of the letter.
"However, the board has concluded that Mr Staley made an error in becoming involved with, and not applying appropriate governance around, the matter, and in taking action to attempt to identify the author of the letter.
"The author of the letter was not identified and no further action was taken."
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 Regulatory 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."
Barclays said the scale of its financial penalty against Mr Staley for the compliance failings would be determined once the regulators' inquiries had concluded. He took home over £4m in the bank's last financial year.
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."
Shares in the FTSE 100 listed bank opened 0.9% lower though later recovered to close 0.4% higher.