The banking giant is to come under the spotlight on Monday over allegations it misled shareholders over the source of funds which averted its need for a bailout at the height of the financial crisis.
Barclays is accused of obscuring the true source of a £3bn investment received in 2008, which the BBC's Panorama alleges came from the Abu Dhabi government rather than Manchester City owner Sheikh Mansour, as the bank had claimed.
The investigation, which will be broadcast on Monday evening, allegedly found that although Barclays was aware the source of funds could change in the run up to a shareholder vote on the deal, that the lender refrained from informing stakeholders until after the transaction was approved.
Even then, disclosure was "buried in the small print", according to Panorama investigators, and used misleading language referring to "his investment".
Although Sheikh Mansour chairs the Abu Dhabi government investment vehicle that provided the funding, International Petroleum Investment Company (IPIC), it is not believed the Emerati royal invested any of his own money in the bank at the time.
Jeremy Carver, a lawyer for Transparency International, told the BBC Barclays may be at fault if government officials benefited from the deal.
The bank told the BBC the mistake was "simply a drafting error" and insisted information given to shareholders following the vote was "entirely appropriate in all the circumstances."
"Immediately following receipt and verification of that information we made overnight amendments to the relevant disclosures relating to the investors in the prospectus documents," said Barclays in a statement.
It added: "The change in ownership of the investing companies had no bearing on the transaction or required approvals."
Barclays avoided nationalisation in 2008 when investors from Abu Dhabi and Qatar agreed to inject £7bn in exchange for a 32pc stake in the bank, a move which the lender said at the time prevented it sinking into a "death spiral ."
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