The British capital began deploying the first of 600 extra armed police officers on Wednesday to counter the threat of terrorism on Wednesday, after the city's police chief warned that it was probably "a case of when not if" an attack hits London.
"Anyone who's been following events in Europe over the past few weeks will understand why we want to show our determination to protect the public," Metropolitan Police chief Bernard Hogan-Howe said as he launched the initiative alongside London Mayor Sadiq Khan.
"The reality of having to deal with armed and deadly attackers is that you need firearms officers who will use force to stop those attackers in their aim," Hogan-Howe said.
Khan said that while Britain's "severe" threat level remains unchanged, "in light of recent deadly attacks in Europe it is important we are prepared should the unthinkable happen."
"We will see more armed officers on our streets, but there is no reason to be alarmed," Khan said. "All of our police officers are playing their part and working closely with all of our communities to prevent the possibility of an attack."
In a statement on Sunday, Hogan-Howe said London's threat level "means an attack is highly likely - you could say it is a case of when not if."