Over several weeks, MI5, along with Scotland Yard and West Midlands Police, had been pursuing the case.
The two men arrested for the plot - Naa'imur Zakariyah Rahman, 20, from north London and Mohammed Aqib Imran, 21, from Birmingham - will attend a preliminary court hearing at Westminster Magistrates' Court on Wednesday morning.
10 Downing Street is the location of the prime minister's office.
It is not clear how Imran and Rahman planned to get through the fortified gates and armed police officers guarding Downing Street.
Showers, high near 53 — TODAY'S FORECAST
It's going to be cold, but it's going to feel even colder as northerly winds whip up to 30 miles per hour in Denver on Wednesday . For Wednesday , expect mostly sunny skies, with a high near 44 and with wind gusts as high as 23 miles per hour .
Addressing the Cabinet, Mr. Parker reportedly said Isis had been defeated in Syria and Iraq but was continuing to orchestrate attacks on the UK.
The details come hours after an independent review suggested the deadly suicide bombing at Manchester Arena may have been prevented if information had been handled differently by British police and intelligence services.
Bomber Salman Abedi killed 22 people when he blew himself up outside an Ariana Grande concert in Manchester.
But Anderson, a former terrorism law reviewer asked by the government to review the recent spate of terror attacks, concluded there is "no cause for despair". The then prime minister, John Major, was inside but was not hurt. The same report found that the ringleader of the June London Bridge attack was actively under investigation at the time.
Security measures were introduced in the 1970s but were increased in the 1980s as the threat from Irish republican groups grew.