In the email exchange reported by the Financial Times, a person pretending to be McFarlane using the email address john.mcfarlane.barclays@gmail.com said Staley owed the chairman "a large scotch" for his defence of the CEO.

A spokesman for Barclays confirmed the contents of the emails, but declined to comment further on the exchange.

McFarlane offered a robust defence of Staley at the lender's annual shareholder meeting in London on Wednesday, after Staley faced calls from individual shareholders to resign after he tried twice to identify the author of a letter about an unnamed senior employee.

Staley initially responded to the emails purportedly from McFarlane with thanks, saying the bank's chairman had "a courage not seen in many people".

"Some day I want to see an ad lib guitar run. You have all the fearlessness of Clapton," Staley said, referring to the guitarist Eric Clapton.

The Financial Times reported the emails were sent by a "prankster" who had a customer issue with Barclays.

The emails ended with the prankster sending a poem, which began "Worry not of tomorrow's end" and ended "Revel in their bloodied eyes", with the first letter of each line spelling out the word "Whistleblower".

Staley replied: "Thanks for sharing the foxhole."

(Reporting by Lawrence White; editing by Susan Thomas)