BBC chief Richard Sharp's position is “increasingly untenable” after a scathing report by cross-party MPs into his role in facilitating a loan guarantee for Boris Johnson.
The under-fire Chairman was accused of making “significant errors of judgement” by acting as a go-between when the ex-Prime Minister found himself in financial difficulty in 2020.
Mr Sharp has admitted to introducing Canadian millionaire Sam Blyth - a distant cousin of Mr Johnson's - to Cabinet Secretary Simon Case. He did not arrange the loan of up to £800,000.
But he was criticised by MPs for failing to declare his role in the "cash for Boris" row when he applying for the job of BBC chairman - which Mr Johnson supported.
In a damning report, the Commons Culture Committee said his actions “constitute a breach of the standards expected of individuals” applying for prominent public appointments - and risked undermining confidence in the BBC.
A spokesman for Mr Sharp said he "regrets" not telling MPs about his involvement with Mr Blyth "and apologises".
He has ordered an internal BBC review over potential conflicts of interests since he joined the corporation.
Boris Johnson previously branded the row "a load of complete nonsense" and said Mr Sharp knew nothing about his finances, adding: "I can tell you that for 100% ding dang sure."
But Labour frontbencher Lisa Nandy told Sky's Ridge on Sunday: “It is a really serious development and it makes Richard Sharp’s position increasingly untenable."
She added: "Increasingly, the circumstances around the relationship between the Conservative Prime Minister, Boris Johnson, and Richard Sharp is looking more and more murky and his position is becoming increasingly untenable as a result."
SNP MP John Nicolson, who sits on the Commons committee, said Mr Sharp's position is now "extremely difficult" and the situation was "all a bit banana republic".
He told BBC: "He has lost the trust of the BBC staff, that's very clear, I've been deluged with messages from BBC staff saying they don't see how he can head up the BBC any more."
Tory minister Andrew Mitchell said the issue was “now a matter for the BBC" - but said “we shouldn’t rush to judgement” when quizzed on Mr Sharp’s position.
"We need to be fair to all parties in this, including Richard Sharp," he said.
"The BBC is not a silent part of all of this, the board of the BBC will need to consider what he's said and reach their own conclusions.
"I think the Government will react appropriately to that."
Tory ex-Culture minister Lord Vaizey defended Mr Sharp, saying: "You can acknowledge it is a blunder without saying it is hanging offence."
A spokesman for Mr Sharp said he "appreciates that there was information that the committee felt that it should have been made aware of in his pre-appointment hearing".
"He regrets this and apologises," the spokesman said.
"It was in seeking at the time to ensure that the rules were followed, and in the belief that this had been achieved, that Mr Sharp acted in good faith in the way he did."
"At that meeting, and subsequently, it was not suggested by the Cabinet Office that the act of connecting Mr Blyth with Mr Case was something that should be declared, and it was explicitly agreed that by not being party to the matter going forward he would be excluded from any conflict."
The spokesman said Mr Sharp "would like to apologise again to the BBC's brilliant staff given the distraction it has caused".
