BBC TV boss Danny Cohen has warned Top Gear's Jeremy Clarkson that "no one person is bigger than the BBC" after a series of headline-making gaffes by the star.
Mr Cohen ordered an internal investigation into the hit show after a string of controversies saw it criticised by communications watchdog Ofcom for breaching broadcasting rules over a ''racial'' term used by Clarkson.
The regulator decided the comment, made by the star during the programme's Burma special screened in March, was offensive.
That came just three months after Clarkson was caught up in another racism row after unaired footage from the programme came to light in which he appeared to use the n-word.
Appearing on Richard Bacon's show on BBC Radio 5 Live, Mr Cohen said he had had several "frank" conversations with Clarkson but refused to say whether the star was on a final warning.
He said: "I've been very clear with what I think is acceptable on the BBC, I've been very clear that no one person is bigger than the BBC."
Asked about the n-word incident, Mr Cohen said: "R egardless of it being on television or not I don't want that stuff going on when we are on production, when you're representing the BBC."
In a letter to the Guardian earlier this month, Mr Cohen said he disagreed with Clarkson's language but insisted the under-fire Top Gear host was not "racist".
The show - and Clarkson - have landed in trouble before. An episode filmed in India was criticised by Indian diplomats and the BBC had to apologise to the Mexican ambassador after remarks made by Clarkson and co-hosts James May and Richard Hammond.
Clarkson was also criticised by mental health charities after he branded people who throw themselves under trains as ''selfish'' and was forced to apologise for telling BBC1's The One Show that striking workers should be shot.