BBC chairman Michael Grade has ordered a report into claims that Today presenter John Humphrys mocked politicians in an after-dinner speech.
John Humphrys has shrugged off the allegations
The Times newspaper said the Radio 4 broadcaster made remarks about Tony Blair, Gordon Brown, and John Prescott in the speech, which was given in June.
A BBC spokesman said Grade had asked director general Mark Thompson for a full report on the claim.
But Humphrys denied being insulting, calling it a "light-hearted" speech.
He is said to have implied all MPs were liars, and claimed former BBC reporter Andrew Gilligan was right in his controversial report that claimed the government "sexed-up" intelligence on Iraq's weapons capabilities to aid the case for war.
After the Hutton report, which led to the resignation of director general Greg Dyke and chairman Gavyn Davies, the BBC apologised to the government for the allegations.
But Humphrys, 62, is said to have told the Communication Directors' Forum on 8 June: "The fact is we got it right."
Humphrys denied mocking politicians, but said of his comments about Gilligan's report: "I was saying nothing that I haven't said many times before in front of countless politicians and reporters."
He said it was "gross misrepresentation" to say he had implied MPs were liars, and added: "Everything I said was meant with great affection for politicians. It was a good humoured, light-hearted speech."
A BBC spokesman said: "Michael Grade has seen reports of what John Humphrys may or may not have said and has asked the director general for a full report including a transcript as soon as possible."