Alleged death threats made against BBC director general Tony Hall are being investigated by the Met Police.
Lord Hall is reported to have received a threatening message after announcing Jeremy Clarkson's contract would not be renewed as he had punched a producer.
The Mail on Sunday also reported Lord Hall and his wife were under 24-hour protection from security guards at their Oxfordshire home.
A BBC spokeswoman said: "We wouldn't comment on security matters."
A Metropolitan Police spokesman said: "Police in Westminster are investigating an allegation of threats to kill. The allegation was reported to police on Wednesday 25 March.
"Inquiries continue. No arrests have been made."
Lord Hall announced his decision on the Top Gear presenter's contract after an internal inquiry found Clarkson had physically and verbally attacked one of the programme's producers, Oisin Tymon, at a North Yorkshire hotel.
The Mail claimed the death threats were made to Lord Hall via email that day. It also published photographs of security guards outside his home.
Mr Tymon, who suffered a split lip, did not file a formal complaint and it is understood Clarkson reported himself to BBC bosses following the incident. He was suspended on 10 March.
The row was said to have occurred because no hot food was provided following a day's filming.
Lord Hall said he had not taken his decision lightly, but insisted "a line has been crossed" and he could not condone what had happened.
The decision caused an outpouring of support from Top Gear fans, with more than a million people signing an online petition to reinstate Clarkson.