Sky News quoted its correspondent as saying there was an "extreme Islamist suicide plot against Downing Street (a reference to the UK Prime Minister's residence)".
Two men will appear in a London court to face terror charges Wednesday after reportedly plotting to assassinate British Prime Minister Theresa May.
According to The Telegraph, details of the alleged terror plot were given to Cabinet members on Tuesday during a briefing by MI5 chief Andrew Parker.
Britain faces the most acute threat ever from Islamist militants seeking to inflict mass attacks, often with spontaneous plots that take just days to bring to execution, the head of the MI5 said in October.
Sky News added that this was something which has been pursued over several weeks at least by Scotland Yard, MI5 and West Midlands Police.
Twenty-year-old north London man Naa'imur Zakariyah Rahman and 21-year-old Mohammed Aqib Imran from south-east Birmingham have been arrested for "intention of committing acts of terrorism" and engaging in conduct in preparation for those acts.
Citing unidentified sources, Sky News reports that the plan, devised by Islamist militants, was stopped with the arrests of two men from the United Kingdom, who've been charged with preparing acts of terrorism. Last week, two men were arrested by armed police and charged with "preparing acts of terrorism".