Top Gear host Jeremy Clarkson has said he is "horrified" that it sounded as though he used racist language while filming an episode and was "begging your forgiveness" for the fact it appeared he did.
Responding to claims that he used the n-word while reciting a nursery rhyme, Clarkson told his Twitter followers he had made every effort to make sure he did not use the slur, but realised it might have sounded as though he had.
In a video posted on his Twitter account tonight, he said: "I was mortified by this, horrified. It is a word I loathe.
"Please be assured I did everything in my power to not use that word. And as I'm sitting here begging your forgiveness for the fact that obviously my efforts weren't quite good enough."
The segment was later edited out of the BBC broadcast.
The BBC also released a firm statement.
"Jeremy Clarkson has set out the background to this regrettable episode," the statement said.
"We have made it absolutely clear to him the standards the BBC expects on-air and off.
"We have left him in no doubt about how seriously we view this."
A solemn-looking Clarkson told his 3.3 million Twitter followers that when reciting the rhyme Eeny, Meeny, Miny Moe..., he "mumbled where the offensive word would normally occur" in two takes, and used the word "teacher" in its place in a third.
"When I viewed this footage, several weeks later, I realised that if you listen very carefully with the sound turned right up, it did appear I actually used the word I was trying to obscure," he added of one of the first two takes.
He said the item was recorded a "couple of years ago" and he "did everything in my power to make sure that that version did not appear in the programme that was transmitted".
Clarkson added that he sent a note to the production office at the time, asking if there was another take that could be used.
The allegations were reported in today's Daily Mirror, which claimed the footage was studied by "audio forensic experts" who told them the star "can be heard chanting Eeny, meeny, miny moe...'. He then mumbles 'Catch a n***** by his toe'".
Earlier today, Clarkson tweeted: "I did not use the n-word. Never use it. The Mirror has gone way too far this time."
His co-host, James May, also came to his defence on Twitter, saying: "Jeremy Clarkson is not a racist. He is a monumental bellend and many other things, but not a racist. I wouldn't work with one."
The claims come days after the motoring show's producer apologised for broadcasting a "light-hearted" joke by Clarkson that sparked a complaint of racism.
An episode, filmed in Burma and Thailand and shown in March, featured a scene in which the presenters built a bridge over the River Kwai, and as an Asian man walked over it Clarkson said: "That is a proud moment, but there's a slope on it."
Somi Guha, an actress who complained to the BBC, said the use of the word "slope" was an example of "casual racism" and "gross misconduct".
The BBC2 show's executive producer Andy Wilman said: "When we used the word slope in the recent Top Gear Burma Special, it was a light-hearted word play joke referencing both the build quality of the bridge and the local Asian man who was crossing it.
"We were not aware at the time, and it has subsequently been brought to our attention, that the word slope is considered by some to be offensive and although it might not be widely recognised in the UK, we appreciate that it can be considered offensive to some here and overseas, for example in Australia and the USA.
"If we had known that at the time, we would not have broadcast the word in this context and regret any offence caused."
Clarkson is well known for courting controversy - in recent years he has been cleared of breaching the broadcasting code by watchdog Ofcom after comparing a Japanese car to people with growths on their faces.
He previously faced a storm of protest from 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.
The motoring show has also faced complaints from Indian and Mexican politicians over remarks made about their countries while filming on location.