Sky's Crime Correspondent Martin Brunt said: "It's the latest in a number of terror plots that police and MI5 believe they've foiled this year.
"I understand that the head of MI5, Andrew Parker, briefed Cabinet ministers today, such is the seriousness of what they believed they have uncovered.
"It is in essence an extreme Islamist suicide plot against Downing Street. Essentially police believe that the plan was to launch some sort of improvised explosive device at Downing Street and in the ensuing chaos attack and kill Theresa May, the Prime Minister. ...