top gearThe Metropolitan Police is investigating alleged death threats made against BBC Director General Tony Hall in the wake of his decision not to renew Top Gear host Jeremy Clarkson’s contract. Hall announced Wednesday that Clarkson would not return to the popular motoring show, following  an inquiry into an altercation between Clarkson and a producer on March 4.

Britain’s The Mail On Sunday reported Hall and his wife have been under 24-hour guard since the alleged threat was sent in the form of an email.

In a statement to Deadline, Scotland Yard confirmed police in Westminster are “investigating an allegation of threats to kill. The allegation was reported to police on Wednesday, 25 March. The threat was made by email. Enquiries continue to establish from where the email was sent, although the content of the message suggests from outside the UK.”

No arrest has been made, the statement said.

Clarkson was suspended March 10, a week after the incident in which he assaulted Oisin Tymon in a Yorkshire hotel. Top Gear was then pulled from the schedule, but Hall said on Wednesday that the broadcaster “must now look to renew Top Gear for 2016. This will be a big challenge and there is no point in pretending otherwise.”

Top Gear has a massive worldwide following; more than one million people signed a petition urging the BBC to retain Clarkson as host.