Naa'imur Zakariyah Rahman from north London was charged with preparing acts of terrorism and was remanded in custody during a hearing at the Westminster Magistrates' Court, the BBC reported.
He appeared alongside 21-year-old Mohammed Aqib Imran, who was accused of trying to join the Islamic State (IS) and preparing acts of terror. Rahman was also charged with assisting Imran in terror planning.
Both men will appear at London's Old Bailey on December 20.
They were arrested in raids by the Metropolitan Police's Counter Terrorism Command in London and Birmingham on November 28. Police believe their plan was to detonate some sort of improvised explosive device (IED) at Downing Street and attack and kill the Prime Minister in the ensuing chaos, Sky News reported.
During the hearing, Rahman gave his nationality as Bangladeshi-British while Imran from Birmingham gave his as Pakistani-British.
The plot was revealed to the British Cabinet on Tuesday by Andrew Parker, the head of the security service MI5, who also told the ministers that security services had foiled nine terrorist attacks in Britain in the past year.
Addressing the Cabinet, Parker reportedly said the IS had been defeated in Syria and Iraq but was continuing to orchestrate attacks on Britain.
After the meeting, the Prime Minister's spokesman said: "The Prime Minister led thanks to the tireless work of staff at MI5 to combat the unprecedented terrorist threat."
"Cabinet ministers heard that while IS suffered major defeats in Iraq and Syria, this did not mean the threat is over. Rather it is spreading to new areas, including trying to encourage attacks in the UK and elsewhere via propaganda on social media," the spokesman added.
Downing Street is protected by armed police officers and separated from the public by fortified gates.
Security measures were introduced in the 1970s but were increased in the 1980s as the threat from Irish republican groups grew.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)