Jeremy Clarkson has instructed lawyers to demand an immediate retraction from the BBC after a senior employee compared him to Jimmy Savile, it has emerged.
The Top Gear host is said to be furious about the "defamatory" smear and is determined to identify the executive behind it.
His friends told the Daily Mail that he believes it was a source connected to the office of former Labour minister James Purnell, now the BBC's £295,000-a-year head of strategy.
The allegations were published in the Mail on Sunday, which quoted a BBC chief "directly involved in the fallout" surrounding Clarkson's suspension following his row with Oisin Tymon, a Top Gear producer, at a North Yorkshire hotel.
The source said that politicians - including the Prime Minister - were turning a blind eye to Clarkson's bad behaviour, in the same way as people once did with Savile, the now notorious paedophile.
"If you look at what David Cameron says or what (former culture and media Secretary) Maria Miller says and you swap Clarkson for Savile, you get this: David Cameron is effectively saying that Savile's a real talent, Maria Miller saying Savile will be Savile," the source was quoted as saying.
Mr Cameron, who is a close friend of Clarkson, has publicly defended the star, saying his children would be heartbroken if Top Gear was taken off air.
A BBC spokesman said: "To suggest that James Purnell is involved is categorically untrue and ridiculous."
Sources have reportedly tried to pin the blame on another well-known senior executive.
Yesterday, the BBC's director-general Lord Hall, insisted that the BBC still needs to determine the facts about Clarkson's "fracas" before making any decisions about his future.
"The most important thing ... is to gather the facts around you and not listen to all the speculation," he said when asked whether Clarkson would lose his job.
Meanwhile, it has emerged that the outspoken star could be back on screen in May, when he has been booked to host satirical news quiz Have I Got News For You.
The BBC is holding an internal investigation into Clarkson's "fracas" with Tymon this week and is expected to announce its decision within days.
Although the television show has been taken off air, Clarkson and his co-hosts Richard Hammond and James May are said to be exploring ways in which they can go ahead with a number of upcoming Top Gear Live arena shows and are determined not to disappoint fans who have paid up to £95 for a ticket.