The terrorists planned to use the ensuing chaos to target and kill Theresa May.
"It is in essence an extreme suicide plot against Downing Street", it said.
It was not clear on Tuesday night what stage the plot was in or if any suspects have been arrested.
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"This is something which has been pursued over several weeks at least by Scotland Yard, MI5 and West Midlands Police".
The two men who were arrested on November 28 for the foiled plot are Naa'imur Zakariyah Rahman, 20, of north London, and Mohammed Aqib Imran, 21, of Birmingham, according to a Metropolitan Police news release.
Imran is charged with preparing acts of terrorism.
MI5 investigators misinterpreted intelligence on Salman Abedi earlier this year and it was disclosed his case was due to be discussed at a meeting scheduled for nine days after his May attack at the Manchester Arena.
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Rahman is charged with assisting Imran in "making preparations for the attack", according to the FT.
Naa'imur Zakariyah Rahman, 20, allegedly had an explosive device in his bag and planned a bomb assault on the prime minister's residence.
In 1991, Irish Republican Army (IRA) militants launched a mortar bomb attack on Number 10.
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