Former BBC director general John Birt has said chairman Richard Sharp’s appointment should not stand as he was an “unsuitable candidate” in a “fatally flawed” process. Lord Birt said the “cosiness” of the £800,000 loan that Sharp facilitated for Boris Johnson makes him unsuitable for the role, despite the BBC chairman denying wrongdoing. Birt, who was director general from 1992 to 2000, told MPs on the House of Commons digital, culture, media and sport committee: “I don’t think his appointment should stand. He’s a person of obvious weight and consequence, but in one vital respect he was an unsuitable candidate, and the appointment process itself was fatally flawed. “The unsuitability came from the very process of navigating a loan for the prime minister at exactly the same time as applying for the job at the BBC. It’s the cosiness of that arrangement that made it unsuitable, and I wish the cabinet secretary had called it out.” Sharp, who is a former Conservative donor, helped his friend Sam Blyth, a distant cousin of Johnson, act as guarantor on the loan after learning of the then prime minister’s financial troubles. Birt also criticised the former cabinet secretary, Simon Case, for failing to dissuade Sharp from making an application to be BBC chairman after learning of his role in the loan, on the grounds that this “disqualified” him. But he said it would be premature to call for Sharp to resign ahead of the publication of a King’s Counsel-led review, while noting that it had “taken quite a long time”. Birt was also asked for his view on Gary Lineker’s tweets criticising government policy, which he said breached the BBC’s “extremely clear” social media guidelines, adding that it was “a serious matter”, which risked undermining the BBC’s “principle of impartiality”. “I don’t think it’s legitimate and right that a BBC presenter of such an important programme should opine,” he said, adding that “the damage isn’t terminal as [the BBC] has too much credit in the bank” and that he hoped an ongoing review of social media guidelines would bring “crystal clarity”. In the session on BBC impartiality, MPs also grilled Chris Patten, a former Conservative party chairman and former chair of the BBC Trust. He agreed with Birt’s views on Sharp: “I think I would find it very difficult to go out and do a news conference defending the BBC’s due impartiality just at the moment if I was in his boots, and I think that’s unfortunate because I think that’s what he should be doing.” Asked whether Sharp should resign, Patten replied: “I don’t think that, were he to do so, I would write a letter of condolence.” However, he disagreed with Birt’s views on Lineker: “I couldn’t understand why people got into such a state of vapours about what he said.” Noting that other prominent presenters, including Lord Sugar, host of The Apprentice, posted political tweets, he said: “It will lead to lots of inconsistencies if you have very strict rules about what anyone making programmes for the BBC can subsequently say about the world.”