Historian Dr David Starkey has said he is being investigated by police over an interview in which he made controversial comments about slavery.
Dr Starkey made the remarks on YouTube to conservative commentator Darren Grimes, who is also being investigated.
Dr Starkey has apologised for saying in June that slavery was not genocide because "so many damn blacks" survived.
He said he did not "intend to stir up racial hatred" and would "defend myself robustly" against the allegation.
The Metropolitan Police said it was investigating "a public order offence relating to a social media video".
In a statement, the TV historian said: "I have apologised unreservedly for the words used and I do so again today. It was a serious error for which I have already paid a significant price.
"I did not, however, intend to stir up racial hatred and there was nothing about the circumstances of the broadcast which made it likely to do so."
Police email 'dismissed as a hoax'
He said he only discovered he was under investigation on Tuesday, six days after the Met sent an email to notify him and Mr Grimes of the action, because the email had not been forwarded on to him.
Scotland Yard sent it to the Bow Group conservative think tank, of which he is vice-president, who thought it was a hoax, he said.
"The effect of this delay and confusion has been to throw the focus of the police investigation wholly on Mr Grimes. This is unfortunate and grossly unfair," Dr Starkey added.
His interviewer was "a young, aspiring journalist and his role in the affair is - at most - secondary", he said, and the focus on him "raised fundamental questions" about the freedom of the press and public debate.
Figures from former home secretary Sajid Javid to ex-Liberal Democrat leader Tim Farron and former director of public prosecutions Lord Macdonald of River Glaven have criticised the investigation into Mr Grimes as a threat to a free media.
No arrests made
In a statement, the Met said: "On July 4, the Metropolitan Police Service was passed an allegation from Durham Police of a public order offence relating to a social media video posted on June 30.
"The matter was reviewed by officers and on July 29 a file was submitted to the Crown Prosecution Service for early investigative advice.
"On September 25 early investigative advice was received and officers began an investigation. This will remain under review. No arrests have been made."
During the original discussion, Dr Starkey said slavery "was not genocide" because "otherwise there wouldn't be so many damn blacks in Africa or Britain would there? An awful lot of them survived."
The subsequent outcry led Cambridge University's Fitzwilliam College, Canterbury Christ Church University, The Mary Rose Trust and publisher HarperCollins to cut ties with him.
Update: On Wednesday the Metropolitan Police said: "On Monday, 12 October a senior officer was appointed to conduct a review of the investigation to ensure it remains proportionate and that all appropriate lines of inquiry are being considered. Whilst this process takes place, two scheduled interviews have been postponed. We remain in contact with the CPS."