Scotland Yard announced on Wednesday that two men had been detained and were due in court later that day on terrorism charges. Britain's domestic security agency MI5 told UK media that it had foiled a plot to assassinate Prime Minister Theresa May.
According to Sky News, "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 attack was characterized as an "extreme Islamist suicide plot." The BBC and several newspapers reported similar stories.
London's Metropolitan Police did not say that the two arrests last week were connected to a Downing Street plot, but simply announced that 20-year-old Naa'imur Zakariyah Rahman of north London and Mohammed Aqib Imran, 21, of Birmingham, were charged with "the intention of committing acts of terrorism," and had already begun preparation for an attack.
The men were arrested by counter-terrorism officers on November 28, and both Imran and Rahman were schedule to appear before Westminster Magistrates' Court on Wednesday.
Independent review: Manchester attack might have been avoided
News of the plot against May came one day after MI5 told a government briefing that it had foiled nine terrorist attacks in the past year.
Britain's security services have undergone both internal and independent reviews after a slew of terror attacks last spring left dozens dead. In London, terrorists used vehicles to drive into pedestrians on Westminster Bridge and London Bridge, killing five and eight bystanders respectively.
A bombing outside an Ariana Grande concert at Manchester Arena on May 22 claimed 23 lives, including the attacker.
David Anderson, the independent investigator who reviewed terror legislation for the UK government from 2011 to 2017, has said that MI5 could have prevented the attack in Manchester if different steps had been taken.
According to the Guardian, Anderson found that the intelligence services had files on suicide bomber Salman Abedi, but that the "significance was not appreciated at the time."
In the weeks leading up to the attack, Abedi was listed as one of 20,000 individuals deemed to have "merited further investigation," but the meeting to discuss these possible threats was scheduled for May 31 — one week after the attack.
"On two separate occasions in the months prior to the attack, intelligence was received by MI5 whose significance was not fully appreciated at the time. It was assessed at the time not to be [related to] terrorism but to possible non-nefarious activity or to criminality on the part of Salman Abedi," said Anderson.
Anderson added the caveat, however, that intelligence services often have massive amounts of information to sort through, and have to make extremely complex decisions in "imperfect" conditions.
MI5 warned Prime Minister May that even with "Islamic State" terrorists being decisively beaten in Iraq and Syria, social media is making it increasingly easy for individuals — especially young men — to be radicalized on their own online.