An Islamist extremist planned to blow up the gates of Downing Street and use pepper spray and a knife to try to kill the prime minister Theresa May, police say.
Naa'imur Zakariyah Rahman, 20, allegedly had an explosive device in his bag and planned a bomb assault on the prime minister's residence.
He was arrested on 28 November and has been charged along with Mohammed Aqib Imran, 21, who police believe was trying to join Isis.
Cabinet members were informed of the plans by MI5 head Andrew Parker, who said nine terror plots had been foiled in the previous 12 months.
Both men will appear in custody at Westminster Magistrates' Court on Wednesday (6 December) charged with terror offences.
The revelations come in the wake of a report that showed the Manchester Arena suicide bomb which left 22 people dead in May could have been averted had "the cards fallen differently".
The report, commissioned by Home Secretary Amber Rudd, looked into the analysis of intelligence by MI5 and counterterrorism police prior to the attacks on Westminster Bridge, London Bridge, the Manchester Arena and Finsbury Park mosque.
The independent report from David Anderson QC found that the Manchester attacker Salman Abedi had been a subject of interest (SOI) for authorities but had been declassified.
This mean he was not under any active investigation although MI5 got more intelligence which should have triggered a fresh probe into his activities.