Footage posted on social media showed anti-lockdown protesters verbally abusing and chasing Nick Watt, the political editor of BBC Newsnight, near Downing Street on Monday.
On Twitter, the prime minister said: “Disgraceful to see the hounding of Nick Watt doing his job.”
“The media must be able to report the facts without fear or favour – they are the lifeblood of our democracy.”
Home secretary Priti Patel also called the video “appalling and distressing”.
Jo Stevens, Labour shadow culture secretary, said: “This extremely disturbing footage showing clear intimidation of a journalist while carrying out his job is absolutely unacceptable and should be condemned in the strongest terms.”
The BBC has also issued a statement, saying: “The safety of journalists is fundamental to any democracy – they must be able to report unhindered, free from abuse. There is absolutely no justification for any journalist to be treated this way.”
The Metropolitan police has launched an investigation on the incident after identifying “a number of possible offences”.
It said: “The behaviour shown in the video is unacceptable. Members of the public, of any profession, have the right to go about their day without being subjected to verbal harassment or actions that put them in fear for their safety.”
“In this instance, while officers were nearby as part of the policing response to the ongoing protest, they were not in the immediate vicinity of the incident.”
The National Union of Journalists (NUJ) told it has asked the Metropolitan police to review its response to the incident, as reported in The Guardian. Police officers can be seen standing in the video as Watt is pursued.
Michelle Stanistreet, the general secretary of the NUJ, said: “It is genuinely shocking that a man escaping a mob screaming at him, shouting traitor and calling him scum, didn’t result in the police immediately intervening. Action should be taken against these thugs. No one should have to tolerate such abusive behaviour and harassment simply for doing their job.”
Watt has not publicly commented on the incident.