BBC Top Gear presenter is accused of using racially offensive term in what appears to be unseen clip from BBC2 show

Jeremy Clarkson has strongly denied allegations he used the N-word in previously unbroadcast footage from the BBC's Top Gear programme.

The presenter was accused by the Daily Mirror of using the language in what appeared to be an unseen clip from the BBC2 show.

In the footage, published on the newspaper's website, Clarkson appears to recite the beginning of the children's nursery rhyme "Eeny, meeny, miny, moe..." before appearing to mumble: "Catch a nigger by his toe."

The BBC on Thursday launched an urgent investigation into the allegations, while Clarkson denied he used the word. He told his 3.2 million Twitter followers: "I did not use the N-word. Never use it. The Mirror has gone way too far this time."

The BBC said: "We've seen the story. The Mirror didn't approach us before publication. Clearly we will establish the facts before commenting."

Amid calls for Clarkson to be sacked, the Mirror reported that it had hired a firm of audio forensic experts to analyse the clip, which it said was taken from the third episode of series 19, which aired in February 2013.

The footage appears to show Clarkson standing between a Toyota GT86 and a Subaru BRZ and saying: "Both cost the same, they have the same bodies and the same interiors with the same equipment. They are even built by the same people in the same factory. You might imagine then that it's quite hard to choose between them, but actually, it isn't. Watch, because this is how you do it."

In the unaired version – which was later passed to the Mirror – the presenter then appears to recite the children's counting rhyme and use the N-word under his breath before pointing at the Toyota and shrugging: "Toyota it is."

The offensive term was removed from the episode eventually shown by the BBC in February 2013, according to the Mirror. In that clip, Clarkson recited the rhyme but this time used the word "teacher".

The allegations come weeks after Top Gear executives expressed regret over a remark made by Clarkson on the show's Burma special, broadcast in March.

During the programme, Clarkson and co-hosts Richard Hammond and James May built a bridge over the river Kwai in Thailand. As an Asian man was seen walking along the bridge, Clarkson said: "That is a proud moment, but there's a slope on it."

The law firm Equal Justice accused the BBC of airing casual racism for using the term "slope", which it said contravened the Equality Act 2010 as it can be used as a derogatory term for people of Asian descent.

Top Gear's executive producer, Andy Wilman, said the remark was meant to be a "light-hearted wordplay joke" and that they were not aware that the term was considered offensive.