Two men were arrested last week following a joint operation by MI5, the UKs counter-terrorism security service, and police.
The two men have been arrested on suspicion of plotting to kill the prime minister by using a bomb disguised as a bag to blow off the gates of Downing Street and then attack her with knives.
The suspects were detained during raids in London and Birmingham last week and charged with terrorism offences. They are due to appear in Westminster Magistrates' Court.
The attack on Westminster in March heralded the start of a spate of attacks, with five terrorist atrocities getting through Britains defences this year and claiming a total of 36 lives in London and Manchester.
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The details of the latest plot emerged as an official report into the terrorist attacks Britain suffered between March and June was released.
The plot was revealed to the Cabinet yesterday by Andrew Parker, the head of MI5, who also told ministers that security services have foiled nine terrorist attacks on the UK in the last year, media reports said.
A Scotland Yard spokesperson declined to confirm that the arrests were linked to a plot to attack May.
It comes as a new report found that security services could possibly have prevented a suicide attack at the Manchester Arena in May. Bomber Salman Abedi killed 22 people when he blew himself up outside an Ariana Grande concert.